123456789_123456789_123456789_123456789_123456789_

Class: Enumerator::Lazy

Relationships & Source Files
Super Chains via Extension / Inclusion / Inheritance
Class Chain:
self, ::Enumerator
Instance Chain:
self, ::Enumerator, ::Enumerable
Inherits: Enumerator
Defined in: enumerator.c

Overview

Lazy

Class Method Summary

::Enumerator - Inherited

.new

Creates a new ::Enumerator object, which can be used as an ::Enumerable.

Instance Attribute Summary

::Enumerable - Included

#all?

Passes each element of the collection to the given block.
#any?

Passes each element of the collection to the given block.
#none?

Passes each element of the collection to the given block.
#one?

Passes each element of the collection to the given block.

Instance Method Summary

::Enumerator - Inherited

#each

Iterates over the block according to how this ::Enumerator was constructed.
#each_with_index

Same as Enumerator#with_index(0), i.e. there is no starting offset.
#each_with_object

Alias for #with_object.
#feed

Sets the value to be returned by the next yield inside e.
#inspect

Creates a printable version of e.
#next

Returns the next object in the enumerator, and move the internal position forward.
#next_values

Returns the next object as an array in the enumerator, and move the internal position forward.
#peek

Returns the next object in the enumerator, but doesn't move the internal position forward.
#peek_values

Returns the next object as an array, similar to #next_values, but doesn't move the internal position forward.
#rewind

Rewinds the enumeration sequence to the beginning.
#size

Returns the size of the enumerator, or nil if it can't be calculated lazily.
#with_index

Iterates the given block for each element with an index, which starts from offset.
#with_object

Iterates the given block for each element with an arbitrary object, obj, and returns obj

::Enumerable - Included

#chunk

Enumerates over the items, chunking them together based on the return value of the block.
#collect

Alias for Enumerable#map.
#collect_concat

Alias for Enumerable#flat_map.
#count

Returns the number of items in enum through enumeration.
#cycle

Calls block for each element of enum repeatedly n times or forever if none or nil is given.
#detect

Alias for Enumerable#find.
#drop

Drops first n elements from enum, and returns rest elements in an array.
#drop_while

Drops elements up to, but not including, the first element for which the block returns nil or false and returns an array containing the remaining elements.
#each_cons

Iterates the given block for each array of consecutive <n> elements.
#each_entry

Calls block once for each element in self, passing that element as a parameter, converting multiple values from yield to an array.
#each_slice

Iterates the given block for each slice of <n> elements.
#each_with_index

Calls block with two arguments, the item and its index, for each item in enum.
#each_with_object

Iterates the given block for each element with an arbitrary object given, and returns the initially given object.
#entries

Alias for Enumerable#to_a.
#find

Passes each entry in enum to block.
#find_all

Alias for Enumerable#select.
#find_index

Compares each entry in enum with value or passes to block.
#first

Returns the first element, or the first n elements, of the enumerable.
#flat_map

Returns a new array with the concatenated results of running block once for every element in enum.
#grep

Returns an array of every element in enum for which Pattern === element.
#group_by

Groups the collection by result of the block.
#include?

Alias for Enumerable#member?.
#inject

Combines all elements of enum by applying a binary operation, specified by a block or a symbol that names a method or operator.
#lazy

Returns a lazy enumerator, whose methods map/collect, flat_map/collect_concat, select/find_all, reject, grep, zip, take, take_while, drop, and drop_while enumerate values only on an as-needed basis.
#map

Returns a new array with the results of running block once for every element in enum.
#max

Returns the object in enum with the maximum value.
#max_by

Returns the object in enum that gives the maximum value from the given block.
#member?

Returns true if any member of enum equals obj.
#min

Returns the object in enum with the minimum value.
#min_by

Returns the object in enum that gives the minimum value from the given block.
#minmax

Returns two elements array which contains the minimum and the maximum value in the enumerable.
#minmax_by

Returns a two element array containing the objects in enum that correspond to the minimum and maximum values respectively from the given block.
#partition

Returns two arrays, the first containing the elements of enum for which the block evaluates to true, the second containing the rest.
#reduce

Alias for Enumerable#inject.
#reject

Returns an array for all elements of enum for which the given block returns false.
#reverse_each

Builds a temporary array and traverses that array in reverse order.
#select

Returns an array containing all elements of enum for which the given block returns a true value.
#slice_after

Creates an enumerator for each chunked elements.
#slice_before

Creates an enumerator for each chunked elements.
#slice_when

Creates an enumerator for each chunked elements.
#sort

Returns an array containing the items in enum sorted, either according to their own <=> method, or by using the results of the supplied block.
#sort_by

Sorts enum using a set of keys generated by mapping the values in enum through the given block.
#take

Returns first n elements from enum.
#take_while

Passes elements to the block until the block returns nil or false, then stops iterating and returns an array of all prior elements.
#to_a

Returns an array containing the items in enum.
#to_h

Returns the result of interpreting enum as a list of [key, value] pairs.
#zip

Takes one element from enum and merges corresponding elements from each args.

Constructor Details

.new(obj, size = nil) {|yielder, *values| ... }

Creates a new Lazy enumerator. When the enumerator is actually enumerated (e.g. by calling #force), obj will be enumerated and each value passed to the given block. The block can yield values back using yielder. For example, to create a method filter_map in both lazy and non-lazy fashions:

module Enumerable
  def filter_map(&block)
    map(&block).compact
  end
end

class Enumerator::Lazy
  def filter_map
    Lazy.new(self) do |yielder, *values|
      result = yield *values
      yielder << result if result
    end
  end
end

(1..Float::INFINITY).lazy.filter_map{|i| i*i if i.even?}.first(5)
    # => [4, 16, 36, 64, 100]

Instance Method Details

#chunk(*args) Also known as: #slice_before, #slice_after, #slice_when

#collect

Alias for #map.

#collect_concat {|obj| ... } ⇒ Lazy #flat_map {|obj| ... } ⇒ Lazy

Alias for #flat_map.

#drop(n)

#drop_while

#to_enum(method = :each, *args) ⇒ Lazy #enum_for(method = :each, *args) ⇒ Lazy #to_enum(method = :each, *args) {|*args| ... } ⇒ Lazy #enum_for(method = :each, *args) {|*args| ... } ⇒ Lazy

Alias for #to_enum.

#find_all

Alias for #select.

#collect_concat {|obj| ... } ⇒ Lazy #flat_map {|obj| ... } ⇒ Lazy
Also known as: #collect_concat

Returns a new lazy enumerator with the concatenated results of running block once for every element in lazy.

["foo", "bar"].lazy.flat_map {|i| i.each_char.lazy}.force
#=> ["f", "o", "o", "b", "a", "r"]

A value x returned by block is decomposed if either of the following conditions is true:

a) <i>x</i> responds to both each and force, which means that
   <i>x</i> is a lazy enumerator.
b) <i>x</i> is an array or responds to to_ary.

Otherwise, x is contained as-is in the return value.

[{a:1}, {b:2}].lazy.flat_map {|i| i}.force
#=> [{:a=>1}, {:b=>2}]

#force(*args) ⇒ Array

Alias for Enumerable#to_a.

#grep(pattern)

#lazy

#map Also known as: #collect

#reject

#select Also known as: #find_all

#slice_after(*args)

Alias for #chunk.

#slice_before(*args)

Alias for #chunk.

#slice_when(*args)

Alias for #chunk.

#take(n)

#take_while

#to_enum(method = :each, *args) ⇒ Lazy #enum_for(method = :each, *args) ⇒ Lazy #to_enum(method = :each, *args) {|*args| ... } ⇒ Lazy #enum_for(method = :each, *args) {|*args| ... } ⇒ Lazy
Also known as: #enum_for

Similar to Object#to_enum, except it returns a lazy enumerator. This makes it easy to define ::Enumerable methods that will naturally remain lazy if called from a lazy enumerator.

For example, continuing from the example in Object#to_enum:

# See Kernel#to_enum for the definition of repeat
r = 1..Float::INFINITY
r.repeat(2).first(5) # => [1, 1, 2, 2, 3]
r.repeat(2).class # => Enumerator
r.repeat(2).map{|n| n ** 2}.first(5) # => endless loop!
# works naturally on lazy enumerator:
r.lazy.repeat(2).class # => Enumerator::Lazy
r.lazy.repeat(2).map{|n| n ** 2}.first(5) # => [1, 1, 4, 4, 9]

#zip(*args)