Class: Hash
| Relationships & Source Files | |
| Super Chains via Extension / Inclusion / Inheritance | |
| Instance Chain: 
          self,
           ::Enumerable | |
| Inherits: | Object | 
| Defined in: | hash.c, hash.c | 
Overview
A Hash maps each of its unique keys to a specific value.
A Hash has certain similarities to an Array, but:
- 
An Array index is always an Integer. 
- 
A Hash key can be (almost) any object. 
Hash Data Syntax
The older syntax for Hash data uses the “hash rocket,” =>:
h = {:foo => 0, : => 1, :baz => 2}
h # => {:foo=>0, :bar=>1, :baz=>2}Alternatively, but only for a Hash key that’s a Symbol, you can use a newer JSON-style syntax, where each bareword becomes a Symbol:
h = {foo: 0, bar: 1, baz: 2}
h # => {:foo=>0, :bar=>1, :baz=>2}You can also use a String in place of a bareword:
h = {'foo': 0, 'bar': 1, 'baz': 2}
h # => {:foo=>0, :bar=>1, :baz=>2}And you can mix the styles:
h = {foo: 0, : => 1, 'baz': 2}
h # => {:foo=>0, :bar=>1, :baz=>2}But it’s an error to try the JSON-style syntax for a key that’s not a bareword or a ::String:
# Raises SyntaxError (syntax error, unexpected ':', expecting =>):
h = {0: 'zero'}Hash value can be omitted, meaning that value will be fetched from the context by the name of the key:
x = 0
y = 100
h = {x:, y:}
h # => {:x=>0, :y=>100}Common Uses
You can use a Hash to give names to objects:
person = {name: 'Matz', language: 'Ruby'}
person # => {:name=>"Matz", :language=>"Ruby"}You can use a Hash to give names to method arguments:
def some_method(hash)
  p hash
end
some_method({foo: 0, bar: 1, baz: 2}) # => {:foo=>0, :bar=>1, :baz=>2}Note: when the last argument in a method call is a Hash, the curly braces may be omitted:
some_method(foo: 0, bar: 1, baz: 2) # => {:foo=>0, :bar=>1, :baz=>2}You can use a Hash to initialize an object:
class Dev
  attr_accessor :name, :language
  def initialize(hash)
    self.name = hash[:name]
    self.language = hash[:language]
  end
end
matz = Dev.new(name: 'Matz', language: 'Ruby')
matz # => #<Dev: @name="Matz", @language="Ruby">Creating a Hash
You can create a Hash object explicitly with:
- 
A hash literal. 
You can convert certain objects to Hashes with:
- 
Method {Kernel.html#method-i-Hash }. 
You can create a Hash by calling method .new.
Create an empty Hash:
h = Hash.new
h # => {}
h.class # => HashYou can create a Hash by calling method .[].
Create an empty Hash:
h = Hash[]
h # => {}Create a Hash with initial entries:
h = Hash[foo: 0, bar: 1, baz: 2]
h # => {:foo=>0, :bar=>1, :baz=>2}You can create a Hash by using its literal form (curly braces).
Create an empty Hash:
h = {}
h # => {}Create a Hash with initial entries:
h = {foo: 0, bar: 1, baz: 2}
h # => {:foo=>0, :bar=>1, :baz=>2}Hash Value Basics
The simplest way to retrieve a Hash value (instance method #[]):
h = {foo: 0, bar: 1, baz: 2}
h[:foo] # => 0The simplest way to create or update a Hash value (instance method #[]=):
h = {foo: 0, bar: 1, baz: 2}
h[:bat] = 3 # => 3
h # => {:foo=>0, :bar=>1, :baz=>2, :bat=>3}
h[:foo] = 4 # => 4
h # => {:foo=>4, :bar=>1, :baz=>2, :bat=>3}The simplest way to delete a Hash entry (instance method #delete):
h = {foo: 0, bar: 1, baz: 2}
h.delete(:) # => 1
h # => {:foo=>0, :baz=>2}Entry Order
A Hash object presents its entries in the order of their creation. This is seen in:
- 
Iterative methods such as #each, #each_key, #each_pair, #each_value. 
- 
Other order-sensitive methods such as #shift, #keys, #values. 
- 
The String returned by method #inspect. 
A new Hash has its initial ordering per the given entries:
h = Hash[foo: 0, bar: 1]
h # => {:foo=>0, :bar=>1}New entries are added at the end:
h[:baz] = 2
h # => {:foo=>0, :bar=>1, :baz=>2}Updating a value does not affect the order:
h[:baz] = 3
h # => {:foo=>0, :bar=>1, :baz=>3}But re-creating a deleted entry can affect the order:
h.delete(:foo)
h[:foo] = 5
h # => {:bar=>1, :baz=>3, :foo=>5}Hash Keys
Hash Key Equivalence
Two objects are treated as the same hash key when their #hash value is identical and the two objects are #eql? to each other.
Modifying an Active Hash Key
Modifying a Hash key while it is in use damages the hash’s index.
This Hash has keys that are Arrays:
a0 = [ :foo, : ]
a1 = [ :baz, :bat ]
h = {a0 => 0, a1 => 1}
h.include?(a0) # => true
h[a0] # => 0
a0.hash # => 110002110Modifying array element a0[0] changes its hash value:
a0[0] = :bam
a0.hash # => 1069447059And damages the Hash index:
h.include?(a0) # => false
h[a0] # => nilYou can repair the hash index using method #rehash:
h.rehash # => {[:bam, :bar]=>0, [:baz, :bat]=>1}
h.include?(a0) # => true
h[a0] # => 0A String key is always safe. That’s because an unfrozen String passed as a key will be replaced by a duplicated and frozen String:
s = 'foo'
s.frozen? # => false
h = {s => 0}
first_key = h.keys.first
first_key.frozen? # => trueUser-Defined Hash Keys
To be useable as a Hash key, objects must implement the methods #hash and #eql?. Note: this requirement does not apply if the Hash uses #compare_by_identity since comparison will then rely on the keys’ object id instead of #hash and #eql?.
Object defines basic implementation for #hash and eq? that makes each object a distinct key. Typically, user-defined classes will want to override these methods to provide meaningful behavior, or for example inherit Struct that has useful definitions for these.
A typical implementation of #hash is based on the object’s data while #eql? is usually aliased to the overridden #== method:
class Book
  attr_reader :, :title
  def initialize(, title)
    @author = 
    @title = title
  end
  def ==(other)
    self.class === other &&
      other. == @author &&
      other.title == @title
  end
  alias eql? ==
  def hash
    @author.hash ^ @title.hash # XOR
  end
end
book1 = Book.new 'matz', 'Ruby in a Nutshell'
book2 = Book.new 'matz', 'Ruby in a Nutshell'
reviews = {}
reviews[book1] = 'Great reference!'
reviews[book2] = 'Nice and compact!'
reviews.length #=> 1Default Values
The methods #[], #values_at and #dig need to return the value associated to a certain key. When that key is not found, that value will be determined by its default proc (if any) or else its default (initially nil).
You can retrieve the default value with method #default:
h = Hash.new
h.default # => nilYou can set the default value by passing an argument to method .new or with method #default=
h = Hash.new(-1)
h.default # => -1
h.default = 0
h.default # => 0This default value is returned for #[], #values_at and #dig when a key is not found:
counts = {foo: 42}
counts.default # => nil (default)
counts[:foo] = 42
counts[:] # => nil
counts.default = 0
counts[:] # => 0
counts.values_at(:foo, :, :baz) # => [42, 0, 0]
counts.dig(:) # => 0Note that the default value is used without being duplicated. It is not advised to set the default value to a mutable object:
synonyms = Hash.new([])
synonyms[:hello] # => []
synonyms[:hello] << :hi # => [:hi], but this mutates the default!
synonyms.default # => [:hi]
synonyms[:world] << :universe
synonyms[:world] # => [:hi, :universe], oops
synonyms.keys # => [], oopsTo use a mutable object as default, it is recommended to use a default proc
Default Proc
When the default proc for a Hash is set (i.e., not nil), the default value returned by method #[] is determined by the default proc alone.
You can retrieve the default proc with method #default_proc:
h = Hash.new
h.default_proc # => nilYou can set the default proc by calling .new with a block or calling the method #default_proc=
h = Hash.new { |hash, key| "Default value for #{key}" }
h.default_proc.class # => Proc
h.default_proc = proc { |hash, key| "Default value for #{key.inspect}" }
h.default_proc.class # => ProcWhen the default proc is set (i.e., not nil) and method #[] is called with with a non-existent key, #[] calls the default proc with both the Hash object itself and the missing key, then returns the proc’s return value:
h = Hash.new { |hash, key| "Default value for #{key}" }
h[:nosuch] # => "Default value for nosuch"Note that in the example above no entry for key :nosuch is created:
h.include?(:nosuch) # => falseHowever, the proc itself can add a new entry:
synonyms = Hash.new { |hash, key| hash[key] = [] }
synonyms.include?(:hello) # => false
synonyms[:hello] << :hi # => [:hi]
synonyms[:world] << :universe # => [:universe]
synonyms.keys # => [:hello, :world]Note that setting the default proc will clear the default value and vice versa.
What’s Here
First, what’s elsewhere. Class Hash:
- 
Inherits from class Object.
- 
Includes module Enumerable, which provides dozens of additional methods.
Here, class Hash provides methods that are useful for:
- 
{#class-Hash-label-Methods+for+Creating+a+Hash Creating a } 
- 
Setting State
- 
Querying
- 
Comparing
- 
Fetching
- 
Assigning
- 
Deleting
- 
Iterating
- 
Converting
- 
Transforming Keys and Values
- 
And more.…
Class Hash also includes methods from module ::Enumerable.
Methods for Creating a Hash
- ::[]
- 
Returns a new hash populated with given objects. 
- ::new
- 
Returns a new empty hash. 
- ::try_convert
- 
Returns a new hash created from a given object. 
Methods for Setting Hash State
- #compare_by_identity
- 
Sets selfto consider only identity in comparing keys.
- #default=
- 
Sets the default to a given value. 
- #default_proc=
- 
Sets the default proc to a given proc. 
- #rehash
- 
Rebuilds the hash table by recomputing the hash index for each key. 
Methods for Querying
- #any?
- 
Returns whether any element satisfies a given criterion. 
- #compare_by_identity?
- 
Returns whether the hash considers only identity when comparing keys. 
- #default
- 
Returns the default value, or the default value for a given key. 
- #default_proc
- 
Returns the default proc. 
- #empty?
- 
Returns whether there are no entries. 
- #eql?
- 
Returns whether a given object is equal to self.
- #hash
- 
Returns the integer hash code. 
- #has_value?
- 
Returns whether a given object is a value in self.
- #include?, #has_key?, #member?, #key?
- 
Returns whether a given object is a key in self.
- #length, #size
- 
Returns the count of entries. 
- #value?
- 
Returns whether a given object is a value in self.
Methods for Comparing
- #<
- 
Returns whether selfis a proper subset of a given object.
- #<=
- 
Returns whether selfis a subset of a given object.
- #==
- 
Returns whether a given object is equal to self.
- #>
- 
Returns whether selfis a proper superset of a given object
- #>=
- 
Returns whether selfis a proper superset of a given object.
Methods for Fetching
- #[]
- 
Returns the value associated with a given key. 
- #assoc
- 
Returns a 2-element array containing a given key and its value. 
- #dig
- 
Returns the object in nested objects that is specified by a given key and additional arguments. 
- #fetch
- 
Returns the value for a given key. 
- #fetch_values
- 
Returns array containing the values associated with given keys. 
- #key
- 
Returns the key for the first-found entry with a given value. 
- #keys
- 
Returns an array containing all keys in self.
- #rassoc
- 
Returns a 2-element array consisting of the key and value of the first-found entry having a given value.
- #values
- 
Returns an array containing all values in self.
- #values_at
- 
Returns an array containing values for given keys. 
Methods for Assigning
- #[]=, #store
- 
Associates a given key with a given value. 
- #merge
- 
Returns the hash formed by merging each given hash into a copy of self.
- #merge!, #update
- 
Merges each given hash into self.
- #replace
- 
Replaces the entire contents of selfwith the contents of a givan hash.
Methods for Deleting
These methods remove entries from self:
- #clear
- 
Removes all entries from self.
- #compact!
- 
Removes all nil-valued entries fromself.
- #delete
- 
Removes the entry for a given key. 
- #delete_if
- 
Removes entries selected by a given block. 
- #filter!, #select!
- 
Keep only those entries selected by a given block. 
- #keep_if
- 
Keep only those entries selected by a given block. 
- #reject!
- 
Removes entries selected by a given block. 
- #shift
- 
Removes and returns the first entry. 
These methods return a copy of self with some entries removed:
- #compact
- 
Returns a copy of selfwith allnil-valued entries removed.
- #except
- 
Returns a copy of selfwith entries removed for specified keys.
- #filter, #select
- 
Returns a copy of selfwith only those entries selected by a given block.
- #reject
- 
Returns a copy of selfwith entries removed as specified by a given block.
- #slice
- 
Returns a hash containing the entries for given keys. 
Methods for Iterating
- #each, #each_pair
- 
Calls a given block with each key-value pair. 
- #each_key
- 
Calls a given block with each key. 
- #each_value
- 
Calls a given block with each value. 
Methods for Converting
- #inspect, #to_s
- 
Returns a new ::Stringcontaining the hash entries.
- #to_a
- 
Returns a new array of 2-element arrays; each nested array contains a key-value pair from self.
- #to_h
- 
Returns selfif a Hash; if a subclass of Hash, returns a Hash containing the entries fromself.
- #to_hash
- 
Returns self.
- #to_proc
- 
Returns a proc that maps a given key to its value. 
Methods for Transforming Keys and Values
- #transform_keys
- 
Returns a copy of selfwith modified keys.
- #transform_keys!
- 
Modifies keys in self
- #transform_values
- 
Returns a copy of selfwith modified values.
- #transform_values!
- 
Modifies values in self.
Other Methods
- #flatten
- 
Returns an array that is a 1-dimensional flattening of self.
- #invert
- 
Returns a hash with the each key-value pair inverted. 
Class Method Summary
- 
    
      .[]  ⇒ Hash 
    
    Returns a new Hash object populated with the given objects, if any. 
- 
    
      .new(default_value = nil)  ⇒ Hash 
    
    constructor
    Returns a new empty Hash object. 
- 
    
      .ruby2_keywords_hash(hash)  ⇒ Hash 
    
    Duplicates a given hash and adds a ruby2_keywords flag. 
- 
    
      .ruby2_keywords_hash?(hash)  ⇒ Boolean 
    
    Checks if a given hash is flagged by Module#ruby2_keywords (or Proc#ruby2_keywords). 
- 
    
      .try_convert(obj)  ⇒ Object, ... 
    
    If objis a Hash object, returnsobj.
Instance Attribute Summary
- 
    
      #compare_by_identity  ⇒ self 
    
    readonly
    Sets selfto consider only identity in comparing keys; two keys are considered the same only if they are the same object; returnsself.
- 
    
      #compare_by_identity?  ⇒ Boolean 
    
    readonly
    Returns trueif #compare_by_identity has been called,falseotherwise.
- 
    
      #default_proc  ⇒ Proc? 
    
    rw
    Returns the default proc for self(seeDefault Values):
- 
    
      #default_proc=(proc)  ⇒ Proc 
    
    rw
    Sets the default proc for selftoproc: (seeDefault Values):
- 
    
      #empty?  ⇒ Boolean 
    
    readonly
    Returns trueif there are no hash entries,falseotherwise:
Instance Method Summary
- 
    
      #<(other_hash)  ⇒ Boolean 
    
    Returns trueif #hash is a proper subset ofother_hash,falseotherwise:
- 
    
      #<=(other_hash)  ⇒ Boolean 
    
    Returns trueif #hash is a subset ofother_hash,falseotherwise:
- 
    
      #==(object)  ⇒ Boolean 
    
    Returns trueif all of the following are true: *objectis a Hash object.
- 
    
      #>(other_hash)  ⇒ Boolean 
    
    Returns trueif #hash is a proper superset ofother_hash,falseotherwise:
- 
    
      #>=(other_hash)  ⇒ Boolean 
    
    Returns trueif #hash is a superset ofother_hash,falseotherwise:
- 
    
      #[](key)  ⇒ value 
    
    Returns the value associated with the given #key, if found: 
- 
    
      #[]=(key, value)  ⇒ value 
      (also: #store)
    
    #store is an alias for []=.
- 
    
      #any?  ⇒ Boolean 
    
    Returns trueif any element satisfies a given criterion;falseotherwise.
- 
    
      #assoc(key)  ⇒ Array? 
    
    If the given #key is found, returns a 2-element Array containing that key and its value: 
- 
    
      #clear  ⇒ self 
    
    Removes all hash entries; returns self.
- 
    
      #compact  ⇒ Hash 
    
    Returns a copy of selfwith allnil-valued entries removed:
- 
    
      #compact!  ⇒ self? 
    
    Returns selfwith all itsnil-valued entries removed (in place):
- #deconstruct_keys(keys)
- 
    
      #default  ⇒ Object 
    
    Returns the default value for the given #key. 
- 
    
      #default=(value)  ⇒ Object 
    
    Sets the default value to value; returnsvalue:
- 
    
      #delete(key)  ⇒ value? 
    
    Deletes the entry for the given #key and returns its associated value. 
- 
    
      #delete_if {|key, value| ... } ⇒ self 
    
    If a block given, calls the block with each key-value pair; deletes each entry for which the block returns a truthy value; returns self:
- 
    
      #dig(key, *identifiers)  ⇒ Object 
    
    Finds and returns the object in nested objects that is specified by #key and identifiers.
- 
    
      #each {|key, value| ... } ⇒ self 
      (also: #each_pair)
    
    eachis an alias for #each_pair.
- 
    
      #each_key {|key| ... } ⇒ self 
    
    Calls the given block with each key; returns self:
- 
    
      #each_pair {|key, value| ... } ⇒ self 
    
    Alias for #each. 
- 
    
      #each_value {|value| ... } ⇒ self 
    
    Calls the given block with each value; returns self:
- 
    
      #eql?(object)  ⇒ Boolean 
    
    Returns trueif all of the following are true: *objectis a Hash object.
- 
    
      #except(*keys)  ⇒ Hash 
    
    Returns a new Hash excluding entries for the given #keys: 
- 
    
      #fetch(key)  ⇒ Object 
    
    Returns the value for the given #key, if found. 
- 
    
      #fetch_values(*keys)  ⇒ Array 
    
    Returns a new Array containing the values associated with the given keys *keys: 
- 
    
      #select {|key, value| ... } ⇒ Hash 
      (also: #select)
    
    filteris an alias for #select.
- 
    
      #select! {|key, value| ... } ⇒ self? 
      (also: #select!)
    
    filter!is an alias for #select!.
- 
    
      #flatten  ⇒ Array 
    
    Returns a new Array object that is a 1-dimensional flattening of self.
- 
    
      #has_key?(key)  ⇒ Boolean 
    
    Alias for #key?. 
- 
    
      #has_value?(value)  ⇒ Boolean 
    
    Alias for #value?. 
- 
    
      #hash  ⇒ Integer 
    
    Returns the Integer hash-code for the hash. 
- 
    
      #include?(key)  ⇒ Boolean 
    
    Alias for #key?. 
- 
    
      #initialize_copy(other_hash)  ⇒ self 
    
    Alias for #replace. 
- 
    
      #inspect  ⇒ String 
    
    Alias for #to_s. 
- 
    
      #invert  ⇒ Hash 
    
    Returns a new Hash object with the each key-value pair inverted: 
- 
    
      #keep_if {|key, value| ... } ⇒ self 
    
    Calls the block for each key-value pair; retains the entry if the block returns a truthy value; otherwise deletes the entry; returns self.
- 
    
      #key(value)  ⇒ key? 
    
    Returns the key for the first-found entry with the given value(seeEntry Order):
- #key?(key) ⇒ Boolean (also: #include?, #member?, #has_key?)
- 
    
      #keys  ⇒ Array 
    
    Returns a new Array containing all keys in self:
- 
    
      #length  ⇒ Integer 
      (also: #size)
    
    Returns the count of entries in self:
- 
    
      #member?(key)  ⇒ Boolean 
    
    Alias for #key?. 
- 
    
      #merge  ⇒ copy_of_self 
    
    Returns the new Hash formed by merging each of other_hashesinto a copy ofself.
- 
    
      #merge!  ⇒ self 
      (also: #update)
    
    Merges each of other_hashesintoself; returnsself.
- 
    
      #rassoc(value)  ⇒ Array? 
    
    Returns a new 2-element Array consisting of the key and value of the first-found entry whose value is #== to value (see Entry Order):
- 
    
      #rehash  ⇒ self 
    
    Rebuilds the hash table by recomputing the hash index for each key; returns self.
- 
    
      #reject {|key, value| ... } ⇒ Hash 
    
    Returns a new Hash object whose entries are all those from selffor which the block returnsfalseornil:
- 
    
      #reject! {|key, value| ... } ⇒ self? 
    
    Returns self, whose remaining entries are those for which the block returnsfalseornil:
- 
    
      #replace(other_hash)  ⇒ self 
      (also: #initialize_copy)
    
    Replaces the entire contents of selfwith the contents ofother_hash; returnsself:
- 
    
      #select {|key, value| ... } ⇒ Hash 
    
    Alias for #filter. 
- 
    
      #select! {|key, value| ... } ⇒ self? 
    
    Alias for #filter!. 
- 
    
      #shift  ⇒ Array, value 
    
    Removes the first hash entry (see Entry Order); returns a 2-element Array containing the removed key and value:
- 
    
      #size  ⇒ Integer 
    
    Alias for #length. 
- 
    
      #slice(*keys)  ⇒ Hash 
    
    Returns a new Hash object containing the entries for the given #keys: 
- 
    
      #store(key, value)  
    
    Alias for #[]=. 
- 
    
      #to_a  ⇒ Array 
    
    Returns a new Array of 2-element Array objects; each nested Array contains a key-value pair from self:
- 
    
      #to_h  ⇒ self, Hash 
    
    For an instance of Hash, returns self.
- 
    
      #to_hash  ⇒ self 
    
    Returns self.
- 
    
      #to_proc  ⇒ Proc 
    
    Returns a Proc object that maps a key to its value: 
- 
    
      #to_s  ⇒ String 
      (also: #inspect)
    
    Returns a new String containing the hash entries: 
- 
    
      #transform_keys {|key| ... } ⇒ Hash 
    
    Returns a new Hash object; each entry has: * A key provided by the block. 
- 
    
      #transform_keys! {|key| ... } ⇒ self 
    
    Same as #transform_keys but modifies the receiver in place instead of returning a new hash. 
- 
    
      #transform_values {|value| ... } ⇒ Hash 
    
    Returns a new Hash object; each entry has: * A key from self.
- 
    
      #transform_values! {|value| ... } ⇒ self 
    
    Returns self, whose keys are unchanged, and whose values are determined by the given block.
- 
    
      #merge!  ⇒ self 
    
    Alias for #merge!. 
- #value?(value) ⇒ Boolean (also: #has_value?)
- 
    
      #values  ⇒ Array 
    
    Returns a new Array containing all values in self:
- 
    
      #values_at(*keys)  ⇒ Array 
    
    Returns a new Array containing values for the given #keys: 
::Enumerable - Included
| #all? | Returns whether every element meets a given criterion. | 
| #any? | Returns whether any element meets a given criterion. | 
| #chain | Returns an enumerator object generated from this enumerator and given enumerables. | 
| #chunk | Each element in the returned enumerator is a 2-element array consisting of: | 
| #chunk_while | Creates an enumerator for each chunked elements. | 
| #collect | Alias for Enumerable#map. | 
| #collect_concat | Alias for Enumerable#flat_map. | 
| #compact | Returns an array of all non- | 
| #count | Returns the count of elements, based on an argument or block criterion, if given. | 
| #cycle | When called with positive integer argument  | 
| #detect | Alias for Enumerable#find. | 
| #drop | For positive integer  | 
| #drop_while | Calls the block with successive elements as long as the block returns a truthy value; returns an array of all elements after that point: | 
| #each_cons | Calls the block with each successive overlapped  | 
| #each_entry | Calls the given block with each element, converting multiple values from yield to an array; returns  | 
| #each_slice | Calls the block with each successive disjoint  | 
| #each_with_index | With a block given, calls the block with each element and its index; returns  | 
| #each_with_object | Calls the block once for each element, passing both the element and the given object: | 
| #entries | Alias for Enumerable#to_a. | 
| #filter | Returns an array containing elements selected by the block. | 
| #filter_map | Returns an array containing truthy elements returned by the block. | 
| #find | Returns the first element for which the block returns a truthy value. | 
| #find_all | Alias for Enumerable#filter. | 
| #find_index | Returns the index of the first element that meets a specified criterion, or  | 
| #first | Returns the first element or elements. | 
| #flat_map | Returns an array of flattened objects returned by the block. | 
| #grep | Returns an array of objects based elements of  | 
| #grep_v | Returns an array of objects based on elements of  | 
| #group_by | With a block given returns a hash: | 
| #include? | Alias for Enumerable#member?. | 
| #inject | Returns an object formed from operands via either: | 
| #lazy | Returns an  | 
| #map | Returns an array of objects returned by the block. | 
| #max | Returns the element with the maximum element according to a given criterion. | 
| #max_by | Returns the elements for which the block returns the maximum values. | 
| #member? | Returns whether for any element  | 
| #min | Returns the element with the minimum element according to a given criterion. | 
| #min_by | Returns the elements for which the block returns the minimum values. | 
| #minmax | Returns a 2-element array containing the minimum and maximum elements according to a given criterion. | 
| #minmax_by | Returns a 2-element array containing the elements for which the block returns minimum and maximum values: | 
| #none? | Returns whether no element meets a given criterion. | 
| #one? | Returns whether exactly one element meets a given criterion. | 
| #partition | With a block given, returns an array of two arrays: | 
| #reduce | Alias for Enumerable#inject. | 
| #reject | Returns an array of objects rejected by the block. | 
| #reverse_each | With a block given, calls the block with each element, but in reverse order; returns  | 
| #select | Alias for Enumerable#filter. | 
| #slice_after | Creates an enumerator for each chunked elements. | 
| #slice_before | With argument  | 
| #slice_when | Creates an enumerator for each chunked elements. | 
| #sort | Returns an array containing the sorted elements of  | 
| #sort_by | With a block given, returns an array of elements of  | 
| #sum | With no block given, returns the sum of  | 
| #take | For non-negative integer  | 
| #take_while | Calls the block with successive elements as long as the block returns a truthy value; returns an array of all elements up to that point: | 
| #tally | Returns a hash containing the counts of equal elements: | 
| #to_a | Returns an array containing the items in  | 
| #to_h | When  | 
| #uniq | With no block, returns a new array containing only unique elements; the array has no two elements  | 
| #zip | With no block given, returns a new array  | 
Constructor Details
    
      .new(default_value = nil)  ⇒ Hash 
      .new {|hash, key| ... } ⇒ Hash 
    
  
Hash 
      .new {|hash, key| ... } ⇒ Hash 
    Returns a new empty Hash object.
The initial default value and initial default proc for the new hash depend on which form above was used. See Default Values.
If neither an argument nor a block given, initializes both the default value and the default proc to nil:
h = Hash.new
h.default # => nil
h.default_proc # => nilIf argument default_value given but no block given, initializes the default value to the given default_value and the default proc to nil:
h = Hash.new(false)
h.default # => false
h.default_proc # => nilIf a block given but no argument, stores the block as the default proc and sets the default value to nil:
h = Hash.new {|hash, key| "Default value for #{key}" }
h.default # => nil
h.default_proc.class # => Proc
h[:nosuch] # => "Default value for nosuch"# File 'hash.c', line 1811
static VALUE
rb_hash_initialize(int argc, VALUE *argv, VALUE hash)
{
    VALUE ifnone;
    rb_hash_modify(hash);
    if (rb_block_given_p()) {
	rb_check_arity(argc, 0, 0);
	ifnone = rb_block_proc();
	SET_PROC_DEFAULT(hash, ifnone);
    }
    else {
	rb_check_arity(argc, 0, 1);
	ifnone = argc == 0 ? Qnil : argv[0];
	RHASH_SET_IFNONE(hash, ifnone);
    }
    return hash;
}
  Class Method Details
    
      .[]  ⇒ Hash 
      .[](hash)  ⇒ Hash 
      .[]([*2_element_arrays] )  ⇒ Hash 
      .[](*objects)  ⇒ Hash 
    
  
Hash 
      .[](hash)  ⇒ Hash 
      .[]([*2_element_arrays] )  ⇒ Hash 
      .[](*objects)  ⇒ Hash 
    Returns a new Hash object populated with the given objects, if any. See .new.
With no argument, returns a new empty Hash.
When the single given argument is a Hash, returns a new Hash populated with the entries from the given Hash, excluding the default value or proc.
h = {foo: 0, bar: 1, baz: 2}
Hash[h] # => {:foo=>0, :bar=>1, :baz=>2}When the single given argument is an Array of 2-element Arrays, returns a new Hash object wherein each 2-element array forms a key-value entry:
Hash[ [ [:foo, 0], [:, 1] ] ] # => {:foo=>0, :bar=>1}When the argument count is an even number; returns a new Hash object wherein each successive pair of arguments has become a key-value entry:
Hash[:foo, 0, :, 1] # => {:foo=>0, :bar=>1}Raises an exception if the argument list does not conform to any of the above.
# File 'hash.c', line 1866
static VALUE
rb_hash_s_create(int argc, VALUE *argv, VALUE klass)
{
    VALUE hash, tmp;
    if (argc == 1) {
        tmp = rb_hash_s_try_convert(Qnil, argv[0]);
	if (!NIL_P(tmp)) {
	    hash = hash_alloc(klass);
            hash_copy(hash, tmp);
	    return hash;
	}
	tmp = rb_check_array_type(argv[0]);
	if (!NIL_P(tmp)) {
	    long i;
	    hash = hash_alloc(klass);
	    for (i = 0; i < RARRAY_LEN(tmp); ++i) {
		VALUE e = RARRAY_AREF(tmp, i);
		VALUE v = rb_check_array_type(e);
		VALUE key, val = Qnil;
		if (NIL_P(v)) {
		    rb_raise(rb_eArgError, "wrong element type %s at %ld (expected array)",
			     rb_builtin_class_name(e), i);
		}
		switch (RARRAY_LEN(v)) {
		  default:
		    rb_raise(rb_eArgError, "invalid number of elements (%ld for 1..2)",
			     RARRAY_LEN(v));
		  case 2:
		    val = RARRAY_AREF(v, 1);
		  case 1:
		    key = RARRAY_AREF(v, 0);
		    rb_hash_aset(hash, key, val);
		}
	    }
	    return hash;
	}
    }
    if (argc % 2 != 0) {
	rb_raise(rb_eArgError, "odd number of arguments for Hash");
    }
    hash = hash_alloc(klass);
    rb_hash_bulk_insert(argc, argv, hash);
    hash_verify(hash);
    return hash;
}
  
    .ruby2_keywords_hash(hash)  ⇒ Hash   
Duplicates a given hash and adds a ruby2_keywords flag. This method is not for casual use; debugging, researching, and some truly necessary cases like deserialization of arguments.
h = {k: 1}
h = Hash.ruby2_keywords_hash(h)
def foo(k: 42)
  k
end
foo(*[h]) #=> 1 with neither a warning or an error# File 'hash.c', line 1986
static VALUE
rb_hash_s_ruby2_keywords_hash(VALUE dummy, VALUE hash)
{
    Check_Type(hash, T_HASH);
    hash = rb_hash_dup(hash);
    RHASH(hash)->basic.flags |= RHASH_PASS_AS_KEYWORDS;
    return hash;
}
  
    .ruby2_keywords_hash?(hash)  ⇒ Boolean   
Checks if a given hash is flagged by Module#ruby2_keywords (or Proc#ruby2_keywords). This method is not for casual use; debugging, researching, and some truly necessary cases like serialization of arguments.
ruby2_keywords def foo(*args)
  Hash.ruby2_keywords_hash?(args.last)
end
foo(k: 1)   #=> true
foo({k: 1}) #=> false# File 'hash.c', line 1964
static VALUE
rb_hash_s_ruby2_keywords_hash_p(VALUE dummy, VALUE hash)
{
    Check_Type(hash, T_HASH);
    return RBOOL(RHASH(hash)->basic.flags & RHASH_PASS_AS_KEYWORDS);
}
  .try_convert(obj) ⇒ Object, ...
If obj is a Hash object, returns obj.
Otherwise if obj responds to :to_hash, calls obj.to_hash and returns the result.
Returns nil if obj does not respond to :to_hash
Raises an exception unless obj.to_hash returns a Hash object.
# File 'hash.c', line 1943
static VALUE
rb_hash_s_try_convert(VALUE dummy, VALUE hash)
{
    return rb_check_hash_type(hash);
}
  Instance Attribute Details
    #compare_by_identity  ⇒ self  (readonly)  
Sets self to consider only identity in comparing keys; two keys are considered the same only if they are the same object; returns self.
By default, these two object are considered to be the same key, so s1 will overwrite s0:
s0 = 'x'
s1 = 'x'
h = {}
h.compare_by_identity? # => false
h[s0] = 0
h[s1] = 1
h # => {"x"=>1}After calling #compare_by_identity, the keys are considered to be different, and therefore do not overwrite each other:
h = {}
h.compare_by_identity # => {}
h.compare_by_identity? # => true
h[s0] = 0
h[s1] = 1
h # => {"x"=>0, "x"=>1}# File 'hash.c', line 4411
VALUE
rb_hash_compare_by_id(VALUE hash)
{
    VALUE tmp;
    st_table *identtable;
    if (rb_hash_compare_by_id_p(hash)) return hash;
    rb_hash_modify_check(hash);
    ar_force_convert_table(hash, __FILE__, __LINE__);
    HASH_ASSERT(RHASH_ST_TABLE_P(hash));
    tmp = hash_alloc(0);
    identtable = rb_init_identtable_with_size(RHASH_SIZE(hash));
    RHASH_ST_TABLE_SET(tmp, identtable);
    rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
    st_free_table(RHASH_ST_TABLE(hash));
    RHASH_ST_TABLE_SET(hash, identtable);
    RHASH_ST_CLEAR(tmp);
    return hash;
}
  
    #compare_by_identity?  ⇒ Boolean  (readonly)  
Returns true if #compare_by_identity has been called, false otherwise.
# File 'hash.c', line 4441
MJIT_FUNC_EXPORTED VALUE
rb_hash_compare_by_id_p(VALUE hash)
{
    return RBOOL(RHASH_ST_TABLE_P(hash) && RHASH_ST_TABLE(hash)->type == &identhash);
}
  #default_proc ⇒ Proc? (rw)
# File 'hash.c', line 2274
static VALUE
rb_hash_default_proc(VALUE hash)
{
    if (FL_TEST(hash, RHASH_PROC_DEFAULT)) {
	return RHASH_IFNONE(hash);
    }
    return Qnil;
}
  #default_proc=(proc) ⇒ Proc (rw)
Sets the default proc for self to proc: (see Default Values):
h = {}
h.default_proc # => nil
h.default_proc = proc { |hash, key| "Default value for #{key}" }
h.default_proc.class # => Proc
h.default_proc = nil
h.default_proc # => nil# File 'hash.c', line 2297
VALUE
rb_hash_set_default_proc(VALUE hash, VALUE proc)
{
    VALUE b;
    rb_hash_modify_check(hash);
    if (NIL_P(proc)) {
	SET_DEFAULT(hash, proc);
	return proc;
    }
    b = rb_check_convert_type_with_id(proc, T_DATA, "Proc", idTo_proc);
    if (NIL_P(b) || !rb_obj_is_proc(b)) {
	rb_raise(rb_eTypeError,
		 "wrong default_proc type %s (expected Proc)",
		 rb_obj_classname(proc));
    }
    proc = b;
    SET_PROC_DEFAULT(hash, proc);
    return proc;
}
  
    #empty?  ⇒ Boolean  (readonly)  
Returns true if there are no hash entries, false otherwise:
{}.empty? # => true
{foo: 0, bar: 1, baz: 2}.empty? # => false# File 'hash.c', line 3030
static VALUE
rb_hash_empty_p(VALUE hash)
{
    return RBOOL(RHASH_EMPTY_P(hash));
}
  Instance Method Details
    #<(other_hash)  ⇒ Boolean   
Returns true if #hash is a proper subset of other_hash, false otherwise:
h1 = {foo: 0, bar: 1}
h2 = {foo: 0, bar: 1, baz: 2}
h1 < h2 # => true
h2 < h1 # => false
h1 < h1 # => false# File 'hash.c', line 4655
static VALUE
rb_hash_lt(VALUE hash, VALUE other)
{
    other = to_hash(other);
    if (RHASH_SIZE(hash) >= RHASH_SIZE(other)) return Qfalse;
    return hash_le(hash, other);
}
  
    #<=(other_hash)  ⇒ Boolean   
Returns true if #hash is a subset of other_hash, false otherwise:
h1 = {foo: 0, bar: 1}
h2 = {foo: 0, bar: 1, baz: 2}
h1 <= h2 # => true
h2 <= h1 # => false
h1 <= h1 # => true# File 'hash.c', line 4636
static VALUE
rb_hash_le(VALUE hash, VALUE other)
{
    other = to_hash(other);
    if (RHASH_SIZE(hash) > RHASH_SIZE(other)) return Qfalse;
    return hash_le(hash, other);
}
  
    #==(object)  ⇒ Boolean   
Returns true if all of the following are true:
- 
objectis a Hash object.
- 
#hash and objecthave the same keys (regardless of order).
- 
For each key #key, hash[key] == object[key].
Otherwise, returns false.
Equal:
h1 = {foo: 0, bar: 1, baz: 2}
h2 = {foo: 0, bar: 1, baz: 2}
h1 == h2 # => true
h3 = {baz: 2, bar: 1, foo: 0}
h1 == h3 # => true# File 'hash.c', line 3807
static VALUE
rb_hash_equal(VALUE hash1, VALUE hash2)
{
    return hash_equal(hash1, hash2, FALSE);
}
  
    #>(other_hash)  ⇒ Boolean   
Returns true if #hash is a proper superset of other_hash, false otherwise:
h1 = {foo: 0, bar: 1, baz: 2}
h2 = {foo: 0, bar: 1}
h1 > h2 # => true
h2 > h1 # => false
h1 > h1 # => false# File 'hash.c', line 4693
static VALUE
rb_hash_gt(VALUE hash, VALUE other)
{
    other = to_hash(other);
    if (RHASH_SIZE(hash) <= RHASH_SIZE(other)) return Qfalse;
    return hash_le(other, hash);
}
  
    #>=(other_hash)  ⇒ Boolean   
Returns true if #hash is a superset of other_hash, false otherwise:
h1 = {foo: 0, bar: 1, baz: 2}
h2 = {foo: 0, bar: 1}
h1 >= h2 # => true
h2 >= h1 # => false
h1 >= h1 # => true# File 'hash.c', line 4674
static VALUE
rb_hash_ge(VALUE hash, VALUE other)
{
    other = to_hash(other);
    if (RHASH_SIZE(hash) < RHASH_SIZE(other)) return Qfalse;
    return hash_le(other, hash);
}
  
    #[](key)  ⇒ value   
# File 'hash.c', line 2110
VALUE
rb_hash_aref(VALUE hash, VALUE key)
{
    st_data_t val;
    if (hash_stlike_lookup(hash, key, &val)) {
        return (VALUE)val;
    }
    else {
        return rb_hash_default_value(hash, key);
    }
}
  
    
      #[]=(key, value)  ⇒ value 
      #store(key, value)  
    
    Also known as: #store
  
value 
      #store(key, value)  
    #store is an alias for []=.
Associates the given value with the given #key; returns value.
If the given #key exists, replaces its value with the given value; the ordering is not affected (see Entry Order):
h = {foo: 0, bar: 1}
h[:foo] = 2 # => 2
h.store(:, 3) # => 3
h # => {:foo=>2, :bar=>3}If #key does not exist, adds the #key and value; the new entry is last in the order (see Entry Order):
h = {foo: 0, bar: 1}
h[:baz] = 2 # => 2
h.store(:bat, 3) # => 3
h # => {:foo=>0, :bar=>1, :baz=>2, :bat=>3}# File 'hash.c', line 2937
VALUE
rb_hash_aset(VALUE hash, VALUE key, VALUE val)
{
    int iter_lev = RHASH_ITER_LEV(hash);
    rb_hash_modify(hash);
    if (RHASH_TABLE_NULL_P(hash)) {
	if (iter_lev > 0) no_new_key();
        ar_alloc_table(hash);
    }
    if (RHASH_TYPE(hash) == &identhash || rb_obj_class(key) != rb_cString) {
	RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset, val);
    }
    else {
	RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset_str, val);
    }
    return val;
}
  
    
      #any?  ⇒ Boolean 
      #any?(object)  ⇒ Boolean 
      #any? {|key, value| ... } ⇒ Boolean 
    
  
Boolean 
      #any?(object)  ⇒ Boolean 
      #any? {|key, value| ... } ⇒ Boolean 
    Returns true if any element satisfies a given criterion; false otherwise.
With no argument and no block, returns true if self is non-empty; false if empty.
With argument object and no block, returns true if for any key #key h.assoc(key) == object:
h = {foo: 0, bar: 1, baz: 2}
h.any?([:, 1]) # => true
h.any?([:, 0]) # => false
h.any?([:baz, 1]) # => falseWith no argument and a block, calls the block with each key-value pair; returns true if the block returns any truthy value, false otherwise:
h = {foo: 0, bar: 1, baz: 2}
h.any? {|key, value| value < 3 } # => true
h.any? {|key, value| value > 3 } # => false# File 'hash.c', line 4537
static VALUE
rb_hash_any_p(int argc, VALUE *argv, VALUE hash)
{
    VALUE args[2];
    args[0] = Qfalse;
    rb_check_arity(argc, 0, 1);
    if (RHASH_EMPTY_P(hash)) return Qfalse;
    if (argc) {
        if (rb_block_given_p()) {
            rb_warn("given block not used");
        }
	args[1] = argv[0];
	rb_hash_foreach(hash, any_p_i_pattern, (VALUE)args);
    }
    else {
	if (!rb_block_given_p()) {
	    /* yields pairs, never false */
	    return Qtrue;
	}
        if (rb_block_pair_yield_optimizable())
	    rb_hash_foreach(hash, any_p_i_fast, (VALUE)args);
	else
	    rb_hash_foreach(hash, any_p_i, (VALUE)args);
    }
    return args[0];
}
  #assoc(key) ⇒ Array?
# File 'hash.c', line 4170
static VALUE
rb_hash_assoc(VALUE hash, VALUE key)
{
    st_table *table;
    const struct st_hash_type *orighash;
    VALUE args[2];
    if (RHASH_EMPTY_P(hash)) return Qnil;
    ar_force_convert_table(hash, __FILE__, __LINE__);
    HASH_ASSERT(RHASH_ST_TABLE_P(hash));
    table = RHASH_ST_TABLE(hash);
    orighash = table->type;
    if (orighash != &identhash) {
	VALUE value;
	struct reset_hash_type_arg ensure_arg;
	struct st_hash_type assochash;
	assochash.compare = assoc_cmp;
	assochash.hash = orighash->hash;
        table->type = &assochash;
	args[0] = hash;
	args[1] = key;
	ensure_arg.hash = hash;
	ensure_arg.orighash = orighash;
	value = rb_ensure(lookup2_call, (VALUE)&args, reset_hash_type, (VALUE)&ensure_arg);
	if (value != Qundef) return rb_assoc_new(key, value);
    }
    args[0] = key;
    args[1] = Qnil;
    rb_hash_foreach(hash, assoc_i, (VALUE)args);
    return args[1];
}
  
    #clear  ⇒ self   
Removes all hash entries; returns self.
# File 'hash.c', line 2862
VALUE
rb_hash_clear(VALUE hash)
{
    rb_hash_modify_check(hash);
    if (RHASH_ITER_LEV(hash) > 0) {
        rb_hash_foreach(hash, clear_i, 0);
    }
    else if (RHASH_AR_TABLE_P(hash)) {
        ar_clear(hash);
    }
    else {
        st_clear(RHASH_ST_TABLE(hash));
        compact_after_delete(hash);
    }
    return hash;
}
  
    #compact  ⇒ Hash   
Returns a copy of self with all nil-valued entries removed:
h = {foo: 0, bar: nil, baz: 2, bat: nil}
h1 = h.compact
h1 # => {:foo=>0, :baz=>2}# File 'hash.c', line 4346
static VALUE
rb_hash_compact(VALUE hash)
{
    VALUE result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
	rb_hash_foreach(hash, set_if_not_nil, result);
    }
    return result;
}
  
    #compact!  ⇒ self?   
Returns self with all its nil-valued entries removed (in place):
h = {foo: 0, bar: nil, baz: 2, bat: nil}
h.compact! # => {:foo=>0, :baz=>2}Returns nil if no entries were removed.
# File 'hash.c', line 4367
static VALUE
rb_hash_compact_bang(VALUE hash)
{
    st_index_t n;
    rb_hash_modify_check(hash);
    n = RHASH_SIZE(hash);
    if (n) {
	rb_hash_foreach(hash, delete_if_nil, hash);
        if (n != RHASH_SIZE(hash))
	    return hash;
    }
    return Qnil;
}
  #deconstruct_keys(keys)
[ GitHub ]# File 'hash.c', line 4726
static VALUE
rb_hash_deconstruct_keys(VALUE hash, VALUE keys)
{
    return hash;
}
  Returns the default value for the given #key. The returned value will be determined either by the default proc or by the default value. See Default Values.
With no argument, returns the current default value:
h = {}
h.default # => nilIf #key is given, returns the default value for #key, regardless of whether that key exists:
h = Hash.new { |hash, key| hash[key] = "No key #{key}"}
h[:foo] = "Hello"
h.default(:foo) # => "No key foo"# File 'hash.c', line 2227
static VALUE
rb_hash_default(int argc, VALUE *argv, VALUE hash)
{
    VALUE ifnone;
    rb_check_arity(argc, 0, 1);
    ifnone = RHASH_IFNONE(hash);
    if (FL_TEST(hash, RHASH_PROC_DEFAULT)) {
	if (argc == 0) return Qnil;
	return call_default_proc(ifnone, hash, argv[0]);
    }
    return ifnone;
}
  #default=(value) ⇒ Object
# File 'hash.c', line 2254
static VALUE
rb_hash_set_default(VALUE hash, VALUE ifnone)
{
    rb_hash_modify_check(hash);
    SET_DEFAULT(hash, ifnone);
    return ifnone;
}
  
    
      #delete(key)  ⇒ value? 
      #delete(key) {|key| ... } ⇒ Object 
    
  
value? 
      #delete(key) {|key| ... } ⇒ Object 
    Deletes the entry for the given #key and returns its associated value.
If no block is given and #key is found, deletes the entry and returns the associated value:
h = {foo: 0, bar: 1, baz: 2}
h.delete(:) # => 1
h # => {:foo=>0, :baz=>2}If no block given and #key is not found, returns nil.
If a block is given and #key is found, ignores the block, deletes the entry, and returns the associated value:
h = {foo: 0, bar: 1, baz: 2}
h.delete(:baz) { |key| raise 'Will never happen'} # => 2
h # => {:foo=>0, :bar=>1}If a block is given and #key is not found, calls the block and returns the block’s return value:
h = {foo: 0, bar: 1, baz: 2}
h.delete(:nosuch) { |key| "Key #{key} not found" } # => "Key nosuch not found"
h # => {:foo=>0, :bar=>1, :baz=>2}# File 'hash.c', line 2430
static VALUE
rb_hash_delete_m(VALUE hash, VALUE key)
{
    VALUE val;
    rb_hash_modify_check(hash);
    val = rb_hash_delete_entry(hash, key);
    if (val != Qundef) {
        compact_after_delete(hash);
	return val;
    }
    else {
	if (rb_block_given_p()) {
	    return rb_yield(key);
	}
	else {
	    return Qnil;
	}
    }
}
  
    
      #delete_if {|key, value| ... } ⇒ self 
      #delete_if  ⇒ Enumerator 
    
  
self 
      #delete_if  ⇒ Enumerator 
    If a block given, calls the block with each key-value pair; deletes each entry for which the block returns a truthy value; returns self:
h = {foo: 0, bar: 1, baz: 2}
h.delete_if {|key, value| value > 0 } # => {:foo=>0}If no block given, returns a new Enumerator:
h = {foo: 0, bar: 1, baz: 2}
e = h.delete_if # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:delete_if>
e.each { |key, value| value > 0 } # => {:foo=>0}# File 'hash.c', line 2554
VALUE
rb_hash_delete_if(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    if (!RHASH_TABLE_EMPTY_P(hash)) {
        rb_hash_foreach(hash, delete_if_i, hash);
        compact_after_delete(hash);
    }
    return hash;
}
  #dig(key, *identifiers) ⇒ Object
Finds and returns the object in nested objects that is specified by #key and identifiers. The nested objects may be instances of various classes. See Dig Methods.
Nested Hashes:
h = {foo: {bar: {baz: 2}}}
h.dig(:foo) # => {:bar=>{:baz=>2}}
h.dig(:foo, :) # => {:baz=>2}
h.dig(:foo, :, :baz) # => 2
h.dig(:foo, :, :BAZ) # => nilNested Hashes and Arrays:
h = {foo: {bar: [:a, :b, :c]}}
h.dig(:foo, :, 2) # => :cThis method will use the default values for keys that are not present:
h = {foo: {bar: [:a, :b, :c]}}
h.dig(:hello) # => nil
h.default_proc = -> (hash, _key) { hash }
h.dig(:hello, :world) # => h
h.dig(:hello, :world, :foo, :, 2) # => :c# File 'hash.c', line 4595
static VALUE
rb_hash_dig(int argc, VALUE *argv, VALUE self)
{
    rb_check_arity(argc, 1, UNLIMITED_ARGUMENTS);
    self = rb_hash_aref(self, *argv);
    if (!--argc) return self;
    ++argv;
    return rb_obj_dig(argc, argv, self, Qnil);
}
  
    
      #each {|key, value| ... } ⇒ self 
      #each_pair {|key, value| ... } ⇒ self 
      #each  ⇒ Enumerator 
      #each_pair  ⇒ Enumerator 
    
    Also known as: #each_pair
  
self 
      #each_pair {|key, value| ... } ⇒ self 
      #each  ⇒ Enumerator 
      #each_pair  ⇒ Enumerator 
    each is an alias for #each_pair.
Calls the given block with each key-value pair; returns self:
h = {foo: 0, bar: 1, baz: 2}
h.each_pair {|key, value| puts "#{key}: #{value}"} # => {:foo=>0, :bar=>1, :baz=>2}Output:
foo: 0
: 1
baz: 2Returns a new Enumerator if no block given:
h = {foo: 0, bar: 1, baz: 2}
e = h.each_pair # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:each_pair>
h1 = e.each {|key, value| puts "#{key}: #{value}"}
h1 # => {:foo=>0, :bar=>1, :baz=>2}Output:
foo: 0
: 1
baz: 2# File 'hash.c', line 3158
static VALUE
rb_hash_each_pair(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    if (rb_block_pair_yield_optimizable())
	rb_hash_foreach(hash, each_pair_i_fast, 0);
    else
	rb_hash_foreach(hash, each_pair_i, 0);
    return hash;
}
  
    
      #each_key {|key| ... } ⇒ self 
      #each_key  ⇒ Enumerator 
    
  
self 
      #each_key  ⇒ Enumerator 
    Calls the given block with each key; returns self:
h = {foo: 0, bar: 1, baz: 2}
h.each_key {|key| puts key }  # => {:foo=>0, :bar=>1, :baz=>2}Output:
foo
bazReturns a new Enumerator if no block given:
h = {foo: 0, bar: 1, baz: 2}
e = h.each_key # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:each_key>
h1 = e.each {|key| puts key }
h1 # => {:foo=>0, :bar=>1, :baz=>2}Output:
foo
baz# File 'hash.c', line 3105
static VALUE
rb_hash_each_key(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_foreach(hash, each_key_i, 0);
    return hash;
}
  
    
      #each {|key, value| ... } ⇒ self 
      #each_pair {|key, value| ... } ⇒ self 
      #each  ⇒ Enumerator 
      #each_pair  ⇒ Enumerator 
    
  
self 
      #each_pair {|key, value| ... } ⇒ self 
      #each  ⇒ Enumerator 
      #each_pair  ⇒ Enumerator 
    Alias for #each.
    
      #each_value {|value| ... } ⇒ self 
      #each_value  ⇒ Enumerator 
    
  
self 
      #each_value  ⇒ Enumerator 
    Calls the given block with each value; returns self:
h = {foo: 0, bar: 1, baz: 2}
h.each_value {|value| puts value } # => {:foo=>0, :bar=>1, :baz=>2}Output:
0
1
2Returns a new Enumerator if no block given:
h = {foo: 0, bar: 1, baz: 2}
e = h.each_value # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:each_value>
h1 = e.each {|value| puts value }
h1 # => {:foo=>0, :bar=>1, :baz=>2}Output:
0
1
2# File 'hash.c', line 3067
static VALUE
rb_hash_each_value(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_foreach(hash, each_value_i, 0);
    return hash;
}
  
    #eql?(object)  ⇒ Boolean   
Returns true if all of the following are true:
- 
objectis a Hash object.
- 
#hash and objecthave the same keys (regardless of order).
- 
For each key #key, h[key] eql? object[key].
Otherwise, returns false.
Equal:
h1 = {foo: 0, bar: 1, baz: 2}
h2 = {foo: 0, bar: 1, baz: 2}
h1.eql? h2 # => true
h3 = {baz: 2, bar: 1, foo: 0}
h1.eql? h3 # => true# File 'hash.c', line 3832
static VALUE
rb_hash_eql(VALUE hash1, VALUE hash2)
{
    return hash_equal(hash1, hash2, TRUE);
}
  
    #except(*keys)  ⇒ Hash   
# File 'hash.c', line 2673
static VALUE
rb_hash_except(int argc, VALUE *argv, VALUE hash)
{
    int i;
    VALUE key, result;
    result = hash_dup_with_compare_by_id(hash);
    for (i = 0; i < argc; i++) {
        key = argv[i];
        rb_hash_delete(result, key);
    }
    compact_after_delete(result);
    return result;
}
  Returns the value for the given #key, if found.
h = {foo: 0, bar: 1, baz: 2}
h.fetch(:) # => 1If #key is not found and no block was given, returns default_value:
{}.fetch(:nosuch, :default) # => :defaultIf #key is not found and a block was given, yields #key to the block and returns the block’s return value:
{}.fetch(:nosuch) {|key| "No key #{key}"} # => "No key nosuch"Raises KeyError if neither default_value nor a block was given.
Note that this method does not use the values of either #default or #default_proc.
# File 'hash.c', line 2165
static VALUE
rb_hash_fetch_m(int argc, VALUE *argv, VALUE hash)
{
    VALUE key;
    st_data_t val;
    long block_given;
    rb_check_arity(argc, 1, 2);
    key = argv[0];
    block_given = rb_block_given_p();
    if (block_given && argc == 2) {
	rb_warn("block supersedes default value argument");
    }
    if (hash_stlike_lookup(hash, key, &val)) {
        return (VALUE)val;
    }
    else {
        if (block_given) {
            return rb_yield(key);
        }
        else if (argc == 1) {
            VALUE desc = rb_protect(rb_inspect, key, 0);
            if (NIL_P(desc)) {
                desc = rb_any_to_s(key);
            }
            desc = rb_str_ellipsize(desc, 65);
            rb_key_err_raise(rb_sprintf("key not found: %"PRIsVALUE, desc), hash, key);
        }
        else {
            return argv[1];
        }
    }
}
  Returns a new Array containing the values associated with the given keys *keys:
h = {foo: 0, bar: 1, baz: 2}
h.fetch_values(:baz, :foo) # => [2, 0]Returns a new empty Array if no arguments given.
When a block is given, calls the block with each missing key, treating the block’s return value as the value for that key:
h = {foo: 0, bar: 1, baz: 2}
values = h.fetch_values(:, :foo, :bad, :bam) {|key| key.to_s}
values # => [1, 0, "bad", "bam"]When no block is given, raises an exception if any given key is not found.
# File 'hash.c', line 2735
static VALUE
rb_hash_fetch_values(int argc, VALUE *argv, VALUE hash)
{
    VALUE result = rb_ary_new2(argc);
    long i;
    for (i=0; i<argc; i++) {
	rb_ary_push(result, rb_hash_fetch(hash, argv[i]));
    }
    return result;
}
  
    
      #select {|key, value| ... } ⇒ Hash 
      #select  ⇒ Enumerator 
    
    Also known as: #select
  
Hash 
      #select  ⇒ Enumerator 
    filter is an alias for #select.
Returns a new Hash object whose entries are those for which the block returns a truthy value:
h = {foo: 0, bar: 1, baz: 2}
h.select {|key, value| value < 2 } # => {:foo=>0, :bar=>1}Returns a new Enumerator if no block given:
h = {foo: 0, bar: 1, baz: 2}
e = h.select # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:select>
e.each {|key, value| value < 2 } # => {:foo=>0, :bar=>1}# File 'hash.c', line 2774
static VALUE
rb_hash_select(VALUE hash)
{
    VALUE result;
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    result = hash_dup_with_compare_by_id(hash);
    if (!RHASH_EMPTY_P(hash)) {
	rb_hash_foreach(result, keep_if_i, result);
        compact_after_delete(result);
    }
    return result;
}
  
    
      #select! {|key, value| ... } ⇒ self? 
      #select!  ⇒ Enumerator 
    
    Also known as: #select!
  
self? 
      #select!  ⇒ Enumerator 
    filter! is an alias for #select!.
Returns self, whose entries are those for which the block returns a truthy value:
h = {foo: 0, bar: 1, baz: 2}
h.select! {|key, value| value < 2 }  => {:foo=>0, :=>1}Returns nil if no entries were removed.
Returns a new Enumerator if no block given:
h = {foo: 0, bar: 1, baz: 2}
e = h.select!  # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:select!>
e.each { |key, value| value < 2 } # => {:foo=>0, :bar=>1}# File 'hash.c', line 2807
static VALUE
rb_hash_select_bang(VALUE hash)
{
    st_index_t n;
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    n = RHASH_SIZE(hash);
    if (!n) return Qnil;
    rb_hash_foreach(hash, keep_if_i, hash);
    if (n == RHASH_SIZE(hash)) return Qnil;
    return hash;
}
  Returns a new Array object that is a 1-dimensional flattening of self.
By default, nested Arrays are not flattened:
h = {foo: 0, bar: [:bat, 3], baz: 2}
h.flatten # => [:foo, 0, :bar, [:bat, 3], :baz, 2]Takes the depth of recursive flattening from Integer argument level:
h = {foo: 0, bar: [:bat, [:baz, [:bat, ]]]}
h.flatten(1) # => [:foo, 0, :bar, [:bat, [:baz, [:bat]]]]
h.flatten(2) # => [:foo, 0, :bar, :bat, [:baz, [:bat]]]
h.flatten(3) # => [:foo, 0, :bar, :bat, :baz, [:bat]]
h.flatten(4) # => [:foo, 0, :bar, :bat, :baz, :bat]When level is negative, flattens all nested Arrays:
h = {foo: 0, bar: [:bat, [:baz, [:bat, ]]]}
h.flatten(-1) # => [:foo, 0, :bar, :bat, :baz, :bat]
h.flatten(-2) # => [:foo, 0, :bar, :bat, :baz, :bat]When level is zero, returns the equivalent of #to_a :
h = {foo: 0, bar: [:bat, 3], baz: 2}
h.flatten(0) # => [[:foo, 0], [:bar, [:bat, 3]], [:baz, 2]]
h.flatten(0) == h.to_a # => true# File 'hash.c', line 4285
static VALUE
rb_hash_flatten(int argc, VALUE *argv, VALUE hash)
{
    VALUE ary;
    rb_check_arity(argc, 0, 1);
    if (argc) {
	int level = NUM2INT(argv[0]);
	if (level == 0) return rb_hash_to_a(hash);
	ary = rb_ary_new_capa(RHASH_SIZE(hash) * 2);
	rb_hash_foreach(hash, flatten_i, ary);
	level--;
	if (level > 0) {
	    VALUE ary_flatten_level = INT2FIX(level);
	    rb_funcallv(ary, id_flatten_bang, 1, &ary_flatten_level);
	}
	else if (level < 0) {
	    /* flatten recursively */
	    rb_funcallv(ary, id_flatten_bang, 0, 0);
	}
    }
    else {
	ary = rb_ary_new_capa(RHASH_SIZE(hash) * 2);
	rb_hash_foreach(hash, flatten_i, ary);
    }
    return ary;
}
  
    
      #include?(key)  ⇒ Boolean 
      #has_key?(key)  ⇒ Boolean 
      #key?(key)  ⇒ Boolean 
      #member?(key)  ⇒ Boolean 
    
  
Boolean 
      #has_key?(key)  ⇒ Boolean 
      #key?(key)  ⇒ Boolean 
      #member?(key)  ⇒ Boolean 
    Alias for #key?.
    
      #has_value?(value)  ⇒ Boolean 
      #value?(value)  ⇒ Boolean 
    
  
Boolean 
      #value?(value)  ⇒ Boolean 
    Alias for #value?.
#hash ⇒ Integer
Returns the Integer hash-code for the hash.
Two Hash objects have the same hash-code if their content is the same (regardless or order):
h1 = {foo: 0, bar: 1, baz: 2}
h2 = {baz: 2, bar: 1, foo: 0}
h2.hash == h1.hash # => true
h2.eql? h1 # => true# File 'hash.c', line 3864
static VALUE
rb_hash_hash(VALUE hash)
{
    st_index_t size = RHASH_SIZE(hash);
    st_index_t hval = rb_hash_start(size);
    hval = rb_hash_uint(hval, (st_index_t)rb_hash_hash);
    if (size) {
	rb_hash_foreach(hash, hash_i, (VALUE)&hval);
    }
    hval = rb_hash_end(hval);
    return ST2FIX(hval);
}
  
    
      #include?(key)  ⇒ Boolean 
      #has_key?(key)  ⇒ Boolean 
      #key?(key)  ⇒ Boolean 
      #member?(key)  ⇒ Boolean 
    
  
Boolean 
      #has_key?(key)  ⇒ Boolean 
      #key?(key)  ⇒ Boolean 
      #member?(key)  ⇒ Boolean 
    Alias for #key?.
    
      #replace(other_hash)  ⇒ self 
      #initialize_copy(other_hash)  ⇒ self 
    
  
self 
      #initialize_copy(other_hash)  ⇒ self 
    Alias for #replace.
Alias for #to_s.
    #invert  ⇒ Hash   
Returns a new Hash object with the each key-value pair inverted:
h = {foo: 0, bar: 1, baz: 2}
h1 = h.invert
h1 # => {0=>:foo, 1=>:bar, 2=>:baz}Overwrites any repeated new keys: (see Entry Order):
h = {foo: 0, bar: 0, baz: 0}
h.invert # => {0=>:baz}# File 'hash.c', line 3899
static VALUE
rb_hash_invert(VALUE hash)
{
    VALUE h = rb_hash_new_with_size(RHASH_SIZE(hash));
    rb_hash_foreach(hash, rb_hash_invert_i, h);
    return h;
}
  
    
      #keep_if {|key, value| ... } ⇒ self 
      #keep_if  ⇒ Enumerator 
    
  
self 
      #keep_if  ⇒ Enumerator 
    Calls the block for each key-value pair; retains the entry if the block returns a truthy value; otherwise deletes the entry; returns self.
h = {foo: 0, bar: 1, baz: 2}
h.keep_if { |key, value| key.start_with?('b') } # => {:bar=>1, :baz=>2}Returns a new Enumerator if no block given:
h = {foo: 0, bar: 1, baz: 2}
e = h.keep_if # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:keep_if>
e.each { |key, value| key.start_with?('b') } # => {:bar=>1, :baz=>2}# File 'hash.c', line 2838
static VALUE
rb_hash_keep_if(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    if (!RHASH_TABLE_EMPTY_P(hash)) {
        rb_hash_foreach(hash, keep_if_i, hash);
    }
    return hash;
}
  #key(value) ⇒ key?
Returns the key for the first-found entry with the given value (see Entry Order):
h = {foo: 0, bar: 2, baz: 2}
h.key(0) # => :foo
h.key(2) # => :barReturns nil if so such value is found.
# File 'hash.c', line 2343
static VALUE
rb_hash_key(VALUE hash, VALUE value)
{
    VALUE args[2];
    args[0] = value;
    args[1] = Qnil;
    rb_hash_foreach(hash, key_i, (VALUE)args);
    return args[1];
}
  
    
      #include?(key)  ⇒ Boolean 
      #has_key?(key)  ⇒ Boolean 
      #key?(key)  ⇒ Boolean 
      #member?(key)  ⇒ Boolean 
    
    Also known as: #include?, #member?, #has_key?
  
Boolean 
      #has_key?(key)  ⇒ Boolean 
      #key?(key)  ⇒ Boolean 
      #member?(key)  ⇒ Boolean 
    # File 'hash.c', line 3668
MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    return RBOOL(hash_stlike_lookup(hash, key, NULL));
}
  #keys ⇒ Array
Returns a new Array containing all keys in self:
h = {foo: 0, bar: 1, baz: 2}
h.keys # => [:foo, :bar, :baz]# File 'hash.c', line 3579
MJIT_FUNC_EXPORTED VALUE
rb_hash_keys(VALUE hash)
{
    st_index_t size = RHASH_SIZE(hash);
    VALUE keys =  rb_ary_new_capa(size);
    if (size == 0) return keys;
    if (ST_DATA_COMPATIBLE_P(VALUE)) {
        RARRAY_PTR_USE_TRANSIENT(keys, ptr, {
            if (RHASH_AR_TABLE_P(hash)) {
                size = ar_keys(hash, ptr, size);
            }
            else {
                st_table *table = RHASH_ST_TABLE(hash);
                size = st_keys(table, ptr, size);
            }
        });
        rb_gc_writebarrier_remember(keys);
	rb_ary_set_len(keys, size);
    }
    else {
	rb_hash_foreach(hash, keys_i, keys);
    }
    return keys;
}
  Also known as: #size
Returns the count of entries in self:
{foo: 0, bar: 1, baz: 2}.length # => 3length is an alias for #size.
# File 'hash.c', line 3009
VALUE
rb_hash_size(VALUE hash)
{
    return INT2FIX(RHASH_SIZE(hash));
}
  
    
      #include?(key)  ⇒ Boolean 
      #has_key?(key)  ⇒ Boolean 
      #key?(key)  ⇒ Boolean 
      #member?(key)  ⇒ Boolean 
    
  
Boolean 
      #has_key?(key)  ⇒ Boolean 
      #key?(key)  ⇒ Boolean 
      #member?(key)  ⇒ Boolean 
    Alias for #key?.
    
      #merge  ⇒ copy_of_self 
      #merge(*other_hashes)  ⇒ Hash 
      #merge(*other_hashes) {|key, old_value, new_value| ... } ⇒ Hash 
    
  
copy_of_self 
      #merge(*other_hashes)  ⇒ Hash 
      #merge(*other_hashes) {|key, old_value, new_value| ... } ⇒ Hash 
    Returns the new Hash formed by merging each of other_hashes into a copy of self.
Each argument in other_hashes must be a Hash.
With arguments and no block:
- 
Returns the new Hash object formed by merging each successive Hash in other_hashesintoself.
- 
Each new-key entry is added at the end. 
- 
Each duplicate-key entry’s value overwrites the previous value. 
Example:
h = {foo: 0, bar: 1, baz: 2}
h1 = {bat: 3, bar: 4}
h2 = {bam: 5, bat:6}
h.merge(h1, h2) # => {:foo=>0, :bar=>4, :baz=>2, :bat=>6, :bam=>5}With arguments and a block:
- 
Returns a new Hash object that is the merge of selfand each given hash.
- 
The given hashes are merged left to right. 
- 
Each new-key entry is added at the end. 
- 
For each duplicate key: - 
Calls the block with the key and the old and new values. 
- 
The block’s return value becomes the new value for the entry. 
 
- 
Example:
h = {foo: 0, bar: 1, baz: 2}
h1 = {bat: 3, bar: 4}
h2 = {bam: 5, bat:6}
h3 = h.merge(h1, h2) { |key, old_value, new_value| old_value + new_value }
h3 # => {:foo=>0, :bar=>5, :baz=>2, :bat=>9, :bam=>5}With no arguments:
- 
Returns a copy of self.
- 
The block, if given, is ignored. 
Example:
h = {foo: 0, bar: 1, baz: 2}
h.merge # => {:foo=>0, :bar=>1, :baz=>2}
h1 = h.merge { |key, old_value, new_value| raise 'Cannot happen' }
h1 # => {:foo=>0, :bar=>1, :baz=>2}# File 'hash.c', line 4114
static VALUE
rb_hash_merge(int argc, VALUE *argv, VALUE self)
{
    return rb_hash_update(argc, argv, copy_compare_by_id(rb_hash_dup(self), self));
}
  
    
      #merge!  ⇒ self 
      #merge!(*other_hashes)  ⇒ self 
      #merge!(*other_hashes) {|key, old_value, new_value| ... } ⇒ self 
    
    Also known as: #update
  
self 
      #merge!(*other_hashes)  ⇒ self 
      #merge!(*other_hashes) {|key, old_value, new_value| ... } ⇒ self 
    Merges each of other_hashes into self; returns self.
Each argument in other_hashes must be a Hash.
Method #update is an alias for #merge!.
With arguments and no block:
- 
Returns self, after the given hashes are merged into it.
- 
The given hashes are merged left to right. 
- 
Each new entry is added at the end. 
- 
Each duplicate-key entry’s value overwrites the previous value. 
Example:
h = {foo: 0, bar: 1, baz: 2}
h1 = {bat: 3, bar: 4}
h2 = {bam: 5, bat:6}
h.merge!(h1, h2) # => {:foo=>0, :bar=>4, :baz=>2, :bat=>6, :bam=>5}With arguments and a block:
- 
Returns self, after the given hashes are merged.
- 
The given hashes are merged left to right. 
- 
Each new-key entry is added at the end. 
- 
For each duplicate key: - 
Calls the block with the key and the old and new values. 
- 
The block’s return value becomes the new value for the entry. 
 
- 
Example:
h = {foo: 0, bar: 1, baz: 2}
h1 = {bat: 3, bar: 4}
h2 = {bam: 5, bat:6}
h3 = h.merge!(h1, h2) { |key, old_value, new_value| old_value + new_value }
h3 # => {:foo=>0, :bar=>5, :baz=>2, :bat=>9, :bam=>5}With no arguments:
- 
Returns self, unmodified.
- 
The block, if given, is ignored. 
Example:
h = {foo: 0, bar: 1, baz: 2}
h.merge # => {:foo=>0, :bar=>1, :baz=>2}
h1 = h.merge! { |key, old_value, new_value| raise 'Cannot happen' }
h1 # => {:foo=>0, :bar=>1, :baz=>2}# File 'hash.c', line 3995
static VALUE
rb_hash_update(int argc, VALUE *argv, VALUE self)
{
    int i;
    bool block_given = rb_block_given_p();
    rb_hash_modify(self);
    for (i = 0; i < argc; i++){
        VALUE hash = to_hash(argv[i]);
        if (block_given) {
            rb_hash_foreach(hash, rb_hash_update_block_i, self);
        }
        else {
            rb_hash_foreach(hash, rb_hash_update_i, self);
        }
    }
    return self;
}
  #rassoc(value) ⇒ Array?
Returns a new 2-element Array consisting of the key and value of the first-found entry whose value is #== to value (see Entry Order):
h = {foo: 0, bar: 1, baz: 1}
h.rassoc(1) # => [:bar, 1]Returns nil if no such value found.
# File 'hash.c', line 4231
static VALUE
rb_hash_rassoc(VALUE hash, VALUE obj)
{
    VALUE args[2];
    args[0] = obj;
    args[1] = Qnil;
    rb_hash_foreach(hash, rassoc_i, (VALUE)args);
    return args[1];
}
  
    #rehash  ⇒ self   
Rebuilds the hash table by recomputing the hash index for each key; returns self.
The hash table becomes invalid if the hash value of a key has changed after the entry was created. See Modifying an Active Hash Key.
# File 'hash.c', line 2024
VALUE
rb_hash_rehash(VALUE hash)
{
    VALUE tmp;
    st_table *tbl;
    if (RHASH_ITER_LEV(hash) > 0) {
	rb_raise(rb_eRuntimeError, "rehash during iteration");
    }
    rb_hash_modify_check(hash);
    if (RHASH_AR_TABLE_P(hash)) {
        tmp = hash_alloc(0);
        ar_alloc_table(tmp);
        rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
        ar_free_and_clear_table(hash);
        ar_copy(hash, tmp);
        ar_free_and_clear_table(tmp);
    }
    else if (RHASH_ST_TABLE_P(hash)) {
        st_table *old_tab = RHASH_ST_TABLE(hash);
        tmp = hash_alloc(0);
        tbl = st_init_table_with_size(old_tab->type, old_tab->num_entries);
        RHASH_ST_TABLE_SET(tmp, tbl);
        rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
        st_free_table(old_tab);
        RHASH_ST_TABLE_SET(hash, tbl);
        RHASH_ST_CLEAR(tmp);
    }
    hash_verify(hash);
    return hash;
}
  
    
      #reject {|key, value| ... } ⇒ Hash 
      #reject  ⇒ Enumerator 
    
  
Hash 
      #reject  ⇒ Enumerator 
    Returns a new Hash object whose entries are all those from self for which the block returns false or nil:
h = {foo: 0, bar: 1, baz: 2}
h1 = h.reject {|key, value| key.start_with?('b') }
h1 # => {:foo=>0}Returns a new Enumerator if no block given:
h = {foo: 0, bar: 1, baz: 2}
e = h.reject # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:reject>
h1 = e.each {|key, value| key.start_with?('b') }
h1 # => {:foo=>0}# File 'hash.c', line 2616
static VALUE
rb_hash_reject(VALUE hash)
{
    VALUE result;
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    result = hash_dup_with_compare_by_id(hash);
    if (!RHASH_EMPTY_P(hash)) {
	rb_hash_foreach(result, delete_if_i, result);
        compact_after_delete(result);
    }
    return result;
}
  
    
      #reject! {|key, value| ... } ⇒ self? 
      #reject!  ⇒ Enumerator 
    
  
self? 
      #reject!  ⇒ Enumerator 
    Returns self, whose remaining entries are those for which the block returns false or nil:
h = {foo: 0, bar: 1, baz: 2}
h.reject! {|key, value| value < 2 } # => {:baz=>2}Returns nil if no entries are removed.
Returns a new Enumerator if no block given:
h = {foo: 0, bar: 1, baz: 2}
e = h.reject! # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:reject!>
e.each {|key, value| key.start_with?('b') } # => {:foo=>0}# File 'hash.c', line 2584
static VALUE
rb_hash_reject_bang(VALUE hash)
{
    st_index_t n;
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify(hash);
    n = RHASH_SIZE(hash);
    if (!n) return Qnil;
    rb_hash_foreach(hash, delete_if_i, hash);
    if (n == RHASH_SIZE(hash)) return Qnil;
    return hash;
}
  
    #replace(other_hash)  ⇒ self     Also known as: #initialize_copy
  
Replaces the entire contents of self with the contents of other_hash; returns self:
h = {foo: 0, bar: 1, baz: 2}
h.replace({bat: 3, bam: 4}) # => {:bat=>3, :bam=>4}# File 'hash.c', line 2968
static VALUE
rb_hash_replace(VALUE hash, VALUE hash2)
{
    rb_hash_modify_check(hash);
    if (hash == hash2) return hash;
    if (RHASH_ITER_LEV(hash) > 0) {
        rb_raise(rb_eRuntimeError, "can't replace hash during iteration");
    }
    hash2 = to_hash(hash2);
    COPY_DEFAULT(hash, hash2);
    if (RHASH_AR_TABLE_P(hash)) {
        ar_free_and_clear_table(hash);
    }
    else {
        st_free_table(RHASH_ST_TABLE(hash));
        RHASH_ST_CLEAR(hash);
    }
    hash_copy(hash, hash2);
    if (RHASH_EMPTY_P(hash2) && RHASH_ST_TABLE_P(hash2)) {
        /* ident hash */
        RHASH_ST_TABLE_SET(hash, st_init_table_with_size(RHASH_TYPE(hash2), 0));
    }
    rb_gc_writebarrier_remember(hash);
    return hash;
}
  
    
      #select {|key, value| ... } ⇒ Hash 
      #select  ⇒ Enumerator 
    
  
Hash 
      #select  ⇒ Enumerator 
    Alias for #filter.
    
      #select! {|key, value| ... } ⇒ self? 
      #select!  ⇒ Enumerator 
    
  
self? 
      #select!  ⇒ Enumerator 
    Alias for #filter!.
    #shift  ⇒ Array, value   
Removes the first hash entry (see Entry Order); returns a 2-element Array containing the removed key and value:
h = {foo: 0, bar: 1, baz: 2}
h.shift # => [:foo, 0]
h # => {:bar=>1, :baz=>2}Returns the default value if the hash is empty (see Default Values).
# File 'hash.c', line 2482
static VALUE
rb_hash_shift(VALUE hash)
{
    struct shift_var var;
    rb_hash_modify_check(hash);
    if (RHASH_AR_TABLE_P(hash)) {
	var.key = Qundef;
	if (RHASH_ITER_LEV(hash) == 0) {
            if (ar_shift(hash, &var.key, &var.val)) {
		return rb_assoc_new(var.key, var.val);
	    }
	}
	else {
            rb_hash_foreach(hash, shift_i_safe, (VALUE)&var);
            if (var.key != Qundef) {
                rb_hash_delete_entry(hash, var.key);
                return rb_assoc_new(var.key, var.val);
            }
        }
    }
    if (RHASH_ST_TABLE_P(hash)) {
        var.key = Qundef;
        if (RHASH_ITER_LEV(hash) == 0) {
            if (st_shift(RHASH_ST_TABLE(hash), &var.key, &var.val)) {
                return rb_assoc_new(var.key, var.val);
            }
        }
        else {
	    rb_hash_foreach(hash, shift_i_safe, (VALUE)&var);
	    if (var.key != Qundef) {
		rb_hash_delete_entry(hash, var.key);
		return rb_assoc_new(var.key, var.val);
	    }
	}
    }
    return rb_hash_default_value(hash, Qnil);
}
  Alias for #length.
    #slice(*keys)  ⇒ Hash   
# File 'hash.c', line 2641
static VALUE
rb_hash_slice(int argc, VALUE *argv, VALUE hash)
{
    int i;
    VALUE key, value, result;
    if (argc == 0 || RHASH_EMPTY_P(hash)) {
        return copy_compare_by_id(rb_hash_new(), hash);
    }
    result = copy_compare_by_id(rb_hash_new_with_size(argc), hash);
    for (i = 0; i < argc; i++) {
	key = argv[i];
	value = rb_hash_lookup2(hash, key, Qundef);
	if (value != Qundef)
	    rb_hash_aset(result, key, value);
    }
    return result;
}
  
    
      #[]=(key, value)  ⇒ value 
      #store(key, value)  
    
  
value 
      #store(key, value)  
    Alias for #[]=.
#to_a ⇒ Array
Returns a new Array of 2-element Array objects; each nested Array contains a key-value pair from self:
h = {foo: 0, bar: 1, baz: 2}
h.to_a # => [[:foo, 0], [:bar, 1], [:baz, 2]]# File 'hash.c', line 3423
static VALUE
rb_hash_to_a(VALUE hash)
{
    VALUE ary;
    ary = rb_ary_new_capa(RHASH_SIZE(hash));
    rb_hash_foreach(hash, to_a_i, ary);
    return ary;
}
  
    
      #to_h  ⇒ self, Hash 
      #to_h {|key, value| ... } ⇒ Hash 
    
  
self, Hash 
      #to_h {|key, value| ... } ⇒ Hash 
    For an instance of Hash, returns self.
For a subclass of Hash, returns a new Hash containing the content of self.
When a block is given, returns a new Hash object whose content is based on the block; the block should return a 2-element Array object specifying the key-value pair to be included in the returned Array:
h = {foo: 0, bar: 1, baz: 2}
h1 = h.to_h {|key, value| [value, key] }
h1 # => {0=>:foo, 1=>:bar, 2=>:baz}# File 'hash.c', line 3550
static VALUE
rb_hash_to_h(VALUE hash)
{
    if (rb_block_given_p()) {
        return rb_hash_to_h_block(hash);
    }
    if (rb_obj_class(hash) != rb_cHash) {
	const VALUE flags = RBASIC(hash)->flags;
        hash = hash_dup(hash, rb_cHash, flags & RHASH_PROC_DEFAULT);
    }
    return hash;
}
  
    #to_hash  ⇒ self   
Returns self.
# File 'hash.c', line 3492
static VALUE
rb_hash_to_hash(VALUE hash)
{
    return hash;
}
  #to_proc ⇒ Proc
Returns a Proc object that maps a key to its value:
h = {foo: 0, bar: 1, baz: 2}
proc = h.to_proc
proc.class # => Proc
proc.call(:foo) # => 0
proc.call(:) # => 1
proc.call(:nosuch) # => nil# File 'hash.c', line 4720
static VALUE
rb_hash_to_proc(VALUE hash)
{
    return rb_func_lambda_new(hash_proc_call, hash, 1, 1);
}
  #to_s ⇒ String Also known as: #inspect
# File 'hash.c', line 3478
static VALUE
rb_hash_inspect(VALUE hash)
{
    if (RHASH_EMPTY_P(hash))
	return rb_usascii_str_new2("{}");
    return rb_exec_recursive(inspect_hash, hash, 0);
}
  
    
      #transform_keys {|key| ... } ⇒ Hash 
      #transform_keys(hash2)  ⇒ Hash 
      #transform_keys(hash2) {|other_key| ... } ⇒ Hash 
      #transform_keys  ⇒ Enumerator 
    
  
Hash 
      #transform_keys(hash2)  ⇒ Hash 
      #transform_keys(hash2) {|other_key| ... } ⇒ Hash 
      #transform_keys  ⇒ Enumerator 
    Returns a new Hash object; each entry has:
- 
A key provided by the block. 
- 
The value from self.
An optional hash argument can be provided to map keys to new keys. Any key not given will be mapped using the provided block, or remain the same if no block is given.
Transform keys:
h = {foo: 0, bar: 1, baz: 2}
h1 = h.transform_keys {|key| key.to_s }
h1 # => {"foo"=>0, "bar"=>1, "baz"=>2}
h.transform_keys(foo: :, bar: :foo)
#=> {bar: 0, foo: 1, baz: 2}
h.transform_keys(foo: :hello, &:to_s)
#=> {:hello=>0, "bar"=>1, "baz"=>2}Overwrites values for duplicate keys:
h = {foo: 0, bar: 1, baz: 2}
h1 = h.transform_keys {|key| :bat }
h1 # => {:bat=>2}Returns a new Enumerator if no block given:
h = {foo: 0, bar: 1, baz: 2}
e = h.transform_keys # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:transform_keys>
h1 = e.each { |key| key.to_s }
h1 # => {"foo"=>0, "bar"=>1, "baz"=>2}# File 'hash.c', line 3236
static VALUE
rb_hash_transform_keys(int argc, VALUE *argv, VALUE hash)
{
    VALUE result;
    struct transform_keys_args transarg = {0};
    argc = rb_check_arity(argc, 0, 1);
    if (argc > 0) {
        transarg.trans = to_hash(argv[0]);
        transarg.block_given = rb_block_given_p();
    }
    else {
        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    }
    result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
        if (transarg.trans) {
            transarg.result = result;
            rb_hash_foreach(hash, transform_keys_hash_i, (VALUE)&transarg);
        }
        else {
            rb_hash_foreach(hash, transform_keys_i, result);
        }
    }
    return result;
}
  
    
      #transform_keys! {|key| ... } ⇒ self 
      #transform_keys!(hash2)  ⇒ self 
      #transform_keys!(hash2) {|other_key| ... } ⇒ self 
      #transform_keys!  ⇒ Enumerator 
    
  
self 
      #transform_keys!(hash2)  ⇒ self 
      #transform_keys!(hash2) {|other_key| ... } ⇒ self 
      #transform_keys!  ⇒ Enumerator 
    Same as #transform_keys but modifies the receiver in place instead of returning a new hash.
# File 'hash.c', line 3276
static VALUE
rb_hash_transform_keys_bang(int argc, VALUE *argv, VALUE hash)
{
    VALUE trans = 0;
    int block_given = 0;
    argc = rb_check_arity(argc, 0, 1);
    if (argc > 0) {
        trans = to_hash(argv[0]);
        block_given = rb_block_given_p();
    }
    else {
        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    }
    rb_hash_modify_check(hash);
    if (!RHASH_TABLE_EMPTY_P(hash)) {
        long i;
        VALUE new_keys = hash_alloc(0);
        VALUE pairs = rb_ary_tmp_new(RHASH_SIZE(hash) * 2);
        rb_hash_foreach(hash, flatten_i, pairs);
        for (i = 0; i < RARRAY_LEN(pairs); i += 2) {
            VALUE key = RARRAY_AREF(pairs, i), new_key, val;
            if (!trans) {
                new_key = rb_yield(key);
            }
            else if ((new_key = rb_hash_lookup2(trans, key, Qundef)) != Qundef) {
                /* use the transformed key */
            }
            else if (block_given) {
                new_key = rb_yield(key);
            }
            else {
                new_key = key;
            }
            val = RARRAY_AREF(pairs, i+1);
            if (!hash_stlike_lookup(new_keys, key, NULL)) {
                rb_hash_stlike_delete(hash, &key, NULL);
            }
            rb_hash_aset(hash, new_key, val);
            rb_hash_aset(new_keys, new_key, Qnil);
        }
        rb_ary_clear(pairs);
        rb_hash_clear(new_keys);
    }
    compact_after_delete(hash);
    return hash;
}
  
    
      #transform_values {|value| ... } ⇒ Hash 
      #transform_values  ⇒ Enumerator 
    
  
Hash 
      #transform_values  ⇒ Enumerator 
    Returns a new Hash object; each entry has:
- 
A key from self.
- 
A value provided by the block. 
Transform values:
h = {foo: 0, bar: 1, baz: 2}
h1 = h.transform_values {|value| value * 100}
h1 # => {:foo=>0, :bar=>100, :baz=>200}Returns a new Enumerator if no block given:
h = {foo: 0, bar: 1, baz: 2}
e = h.transform_values # => #<Enumerator: {:foo=>0, :bar=>1, :baz=>2}:transform_values>
h1 = e.each { |value| value * 100}
h1 # => {:foo=>0, :bar=>100, :baz=>200}# File 'hash.c', line 3361
static VALUE
rb_hash_transform_values(VALUE hash)
{
    VALUE result;
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    result = hash_dup_with_compare_by_id(hash);
    SET_DEFAULT(result, Qnil);
    if (!RHASH_EMPTY_P(hash)) {
        rb_hash_stlike_foreach_with_replace(result, transform_values_foreach_func, transform_values_foreach_replace, result);
        compact_after_delete(result);
    }
    return result;
}
  
    
      #transform_values! {|value| ... } ⇒ self 
      #transform_values!  ⇒ Enumerator 
    
  
self 
      #transform_values!  ⇒ Enumerator 
    Returns self, whose keys are unchanged, and whose values are determined by the given block.
h = {foo: 0, bar: 1, baz: 2}
h.transform_values! {|value| value * 100} # => {:foo=>0, :bar=>100, :baz=>200}Returns a new Enumerator if no block given:
h = {foo: 0, bar: 1, baz: 2}
e = h.transform_values! # => #<Enumerator: {:foo=>0, :bar=>100, :baz=>200}:transform_values!>
h1 = e.each {|value| value * 100}
h1 # => {:foo=>0, :bar=>100, :baz=>200}# File 'hash.c', line 3393
static VALUE
rb_hash_transform_values_bang(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    if (!RHASH_TABLE_EMPTY_P(hash)) {
        rb_hash_stlike_foreach_with_replace(hash, transform_values_foreach_func, transform_values_foreach_replace, hash);
    }
    return hash;
}
  
    
      #merge!  ⇒ self 
      #merge!(*other_hashes)  ⇒ self 
      #merge!(*other_hashes) {|key, old_value, new_value| ... } ⇒ self 
    
  
self 
      #merge!(*other_hashes)  ⇒ self 
      #merge!(*other_hashes) {|key, old_value, new_value| ... } ⇒ self 
    Alias for #merge!.
    
      #has_value?(value)  ⇒ Boolean 
      #value?(value)  ⇒ Boolean 
    
    Also known as: #has_value?
  
Boolean 
      #value?(value)  ⇒ Boolean 
    ::Method #value? is an alias for #has_value?.
Returns true if value is a value in self, otherwise false.
# File 'hash.c', line 3696
static VALUE
rb_hash_has_value(VALUE hash, VALUE val)
{
    VALUE data[2];
    data[0] = Qfalse;
    data[1] = val;
    rb_hash_foreach(hash, rb_hash_search_value, (VALUE)data);
    return data[0];
}
  #values ⇒ Array
Returns a new Array containing all values in self:
h = {foo: 0, bar: 1, baz: 2}
h.values # => [0, 1, 2]# File 'hash.c', line 3623
VALUE
rb_hash_values(VALUE hash)
{
    VALUE values;
    st_index_t size = RHASH_SIZE(hash);
    values = rb_ary_new_capa(size);
    if (size == 0) return values;
    if (ST_DATA_COMPATIBLE_P(VALUE)) {
        if (RHASH_AR_TABLE_P(hash)) {
            rb_gc_writebarrier_remember(values);
            RARRAY_PTR_USE_TRANSIENT(values, ptr, {
                size = ar_values(hash, ptr, size);
            });
        }
        else if (RHASH_ST_TABLE_P(hash)) {
            st_table *table = RHASH_ST_TABLE(hash);
            rb_gc_writebarrier_remember(values);
            RARRAY_PTR_USE_TRANSIENT(values, ptr, {
                size = st_values(table, ptr, size);
            });
        }
	rb_ary_set_len(values, size);
    }
    else {
	rb_hash_foreach(hash, values_i, values);
    }
    return values;
}
  #values_at(*keys) ⇒ Array
Returns a new Array containing values for the given #keys:
h = {foo: 0, bar: 1, baz: 2}
h.values_at(:baz, :foo) # => [2, 0]The default values are returned for any keys that are not found:
h.values_at(:hello, :foo) # => [nil, 0]# File 'hash.c', line 2703
static VALUE
rb_hash_values_at(int argc, VALUE *argv, VALUE hash)
{
    VALUE result = rb_ary_new2(argc);
    long i;
    for (i=0; i<argc; i++) {
	rb_ary_push(result, rb_hash_aref(hash, argv[i]));
    }
    return result;
}