Class: BasicObject
Relationships & Source Files | |
Super Chains via Extension / Inclusion / Inheritance | |
Class Chain:
self,
Qnil
|
|
Instance Chain:
self,
Qnil
|
|
Inherits: |
Qnil
|
Defined in: | class.c, gc.c, object.c, vm_eval.c |
Overview
BasicObject
is the parent class of all classes in Ruby. In particular, BasicObject
is the parent class of class ::Object
, which is itself the default parent class of every Ruby class:
class Foo; end
Foo.superclass # => Object
Object.superclass # => BasicObject
BasicObject
is the only class that has no parent:
BasicObject.superclass # => nil
Class BasicObject
can be used to create an object hierarchy (e.g., class Delegator) that is independent of Ruby’s object hierarchy. Such objects:
-
Do not have namespace “pollution” from the many methods provided in class Object and its included module Kernel.
-
Do not have definitions of common classes, and so references to such common classes must be fully qualified (
::String
, not::String
).
A variety of strategies can be used to provide useful portions of the Standard Library in subclasses of BasicObject
:
-
The immediate subclass could
include Kernel
, which would define methods such asputs
,exit
, etc. -
A custom Kernel-like module could be created and included.
-
Delegation can be used via #method_missing:
class MyObjectSystem < BasicObject DELEGATE = [:puts, :p] def method_missing(name, *args, &block) return super unless DELEGATE.include? name ::Kernel.send(name, *args, &block) end def respond_to_missing?(name, include_private = false) DELEGATE.include?(name) end end
What’s Here
These are the methods defined for BasicObject:
-
.new: Returns a new BasicObject instance.
-
#!: Returns the boolean negation of
self
:true
orfalse
. -
#!=: Returns whether
self
and the given object are not equal. -
#==: Returns whether
self
and the given object are equivalent. -
#__id__: Returns the integer object identifier for
self
. -
#__send__: Calls the method identified by the given symbol.
-
#equal?: Returns whether
self
and the given object are the same object. -
#instance_eval: Evaluates the given string or block in the context of
self
. -
#instance_exec: Executes the given block in the context of
self
, passing the given arguments. -
#method_missing: Called when
self
is called with a method it does not define. -
#singleton_method_added: Called when a singleton method is added to
self
. -
#singleton_method_removed: Called when a singleton method is removed from
self
. -
#singleton_method_undefined: Called when a singleton method is undefined in
self
.
Class Method Summary
- .new constructor private
Instance Method Summary
-
#! ⇒ Boolean
Boolean negate.
-
#!=(other) ⇒ Boolean
Returns true if two objects are not-equal, otherwise false.
- #==(other) ⇒ Boolean (also: #equal?)
-
#__id__ ⇒ Integer
Returns an integer identifier for
obj
. -
#__send__(symbol [, args...]) ⇒ Object
Invokes the method identified by symbol, passing it any arguments specified.
-
#equal?(other) ⇒ Boolean
Alias for #==.
-
#instance_eval(string [, filename [, lineno]] ) ⇒ Object
Evaluates a string containing Ruby source code, or the given block, within the context of the receiver (obj).
-
#instance_exec(arg...) {|var...| ... } ⇒ Object
Executes the given block within the context of the receiver (obj).
-
#method_missing(symbol [, *args] ) ⇒ result
private
Invoked by Ruby when obj is sent a message it cannot handle.
-
#singleton_method_added(symbol)
private
Invoked as a callback whenever a singleton method is added to the receiver.
-
#singleton_method_removed(symbol)
private
Invoked as a callback whenever a singleton method is removed from the receiver.
-
#singleton_method_undefined(symbol)
private
Invoked as a callback whenever a singleton method is undefined in the receiver.
Constructor Details
.new (private)
[ GitHub ]Dynamic Method Handling
This class handles dynamic methods through the method_missing method
#method_missing(symbol [, *args] ) ⇒ result
(private)
Invoked by Ruby when obj is sent a message it cannot handle. symbol is the symbol for the method called, and args are any arguments that were passed to it. By default, the interpreter raises an error when this method is called. However, it is possible to override the method to provide more dynamic behavior. If it is decided that a particular method should not be handled, then super should be called, so that ancestors can pick up the missing method. The example below creates a class Roman
, which responds to methods with names consisting of roman numerals, returning the corresponding integer values.
class Roman
def roman_to_int(str)
# ...
end
def method_missing(symbol, *args)
str = symbol.id2name
begin
roman_to_int(str)
rescue
super(symbol, *args)
end
end
end
r = Roman.new
r.iv #=> 4
r.xxiii #=> 23
r.mm #=> 2000
r.foo #=> NoMethodError
# File 'vm_eval.c', line 918
static VALUE rb_method_missing(int argc, const VALUE *argv, VALUE obj) { rb_execution_context_t *ec = GET_EC(); raise_method_missing(ec, argc, argv, obj, ec->method_missing_reason); UNREACHABLE_RETURN(Qnil); }
Instance Method Details
#! ⇒ Boolean
Boolean negate.
# File 'object.c', line 263
VALUE rb_obj_not(VALUE obj) { return RBOOL(!RTEST(obj)); }
#!=(other) ⇒ Boolean
Returns true if two objects are not-equal, otherwise false.
# File 'object.c', line 279
VALUE rb_obj_not_equal(VALUE obj1, VALUE obj2) { VALUE result = rb_funcall(obj1, id_eq, 1, obj2); return rb_obj_not(result); }
#==(other) ⇒ Boolean
#equal?(other) ⇒ Boolean
#eql?(other) ⇒ Boolean
Also known as: #equal?
Boolean
#equal?(other) ⇒ Boolean
#eql?(other) ⇒ Boolean
Equality — At the ::Object
level, #==
returns true
only if obj
and other
are the same object. Typically, this method is overridden in descendant classes to provide class-specific meaning.
Unlike #==
, the #equal? method should never be overridden by subclasses as it is used to determine object identity (that is, a.equal?(b)
if and only if a
is the same object as b
):
obj = "a"
other = obj.dup
obj == other #=> true
obj.equal? other #=> false
obj.equal? obj #=> true
The #eql?
method returns true
if obj
and other
refer to the same hash key. This is used by ::Hash
to test members for equality. For any pair of objects where #eql?
returns true
, the #hash
value of both objects must be equal. So any subclass that overrides #eql?
should also override #hash
appropriately.
For objects of class ::Object
, #eql?
is synonymous with #==
. Subclasses normally continue this tradition by aliasing #eql?
to their overridden #==
method, but there are exceptions. ::Numeric
types, for example, perform type conversion across #==
, but not across #eql?
, so:
1 == 1.0 #=> true
1.eql? 1.0 #=> false
# File 'object.c', line 245
VALUE rb_obj_equal(VALUE obj1, VALUE obj2) { return RBOOL(obj1 == obj2); }
Returns an integer identifier for obj
.
The same number will be returned on all calls to object_id
for a given object, and no two active objects will share an id.
Note: that some objects of builtin classes are reused for optimization. This is the case for immediate values and frozen string literals.
BasicObject
implements __id__
, ::Kernel
implements object_id
.
Immediate values are not passed by reference but are passed by value: nil
, true
, false
, Fixnums, Symbols, and some Floats.
Object.new.object_id == Object.new.object_id # => false
(21 * 2).object_id == (21 * 2).object_id # => true
"hello".object_id == "hello".object_id # => false
"hi".freeze.object_id == "hi".freeze.object_id # => true
# File 'gc.c', line 1723
VALUE rb_obj_id(VALUE obj) { /* If obj is an immediate, the object ID is obj directly converted to a Numeric. * Otherwise, the object ID is a Numeric that is a non-zero multiple of * (RUBY_IMMEDIATE_MASK + 1) which guarantees that it does not collide with * any immediates. */ return rb_find_object_id(rb_gc_get_objspace(), obj, rb_gc_impl_object_id); }
Invokes the method identified by symbol, passing it any arguments specified. When the method is identified by a string, the string is converted to a symbol.
BasicObject
implements __send__
, ::Kernel
implements send
. __send__
is safer than send
when obj has the same method name like Socket
. See also public_send
.
class Klass
def hello(*args)
"Hello " + args.join(' ')
end
end
k = Klass.new
k.send :hello, "gentle", "readers" #=> "Hello gentle readers"
# File 'vm_eval.c', line 1307
VALUE rb_f_send(int argc, VALUE *argv, VALUE recv) { return send_internal_kw(argc, argv, recv, CALL_FCALL); }
#==(other) ⇒ Boolean
#equal?(other) ⇒ Boolean
#eql?(other) ⇒ Boolean
Boolean
#equal?(other) ⇒ Boolean
#eql?(other) ⇒ Boolean
Alias for #==.
Evaluates a string containing Ruby source code, or the given block, within the context of the receiver (obj). In order to set the context, the variable self
is set to obj while the code is executing, giving the code access to obj’s instance variables and private methods.
When instance_eval
is given a block, obj is also passed in as the block’s only argument.
When instance_eval
is given a ::String
, the optional second and third parameters supply a filename and starting line number that are used when reporting compilation errors.
class KlassWithSecret
def initialize
@secret = 99
end
private
def the_secret
"Ssssh! The secret is #{@secret}."
end
end
k = KlassWithSecret.new
k.instance_eval { @secret } #=> 99
k.instance_eval { the_secret } #=> "Ssssh! The secret is 99."
k.instance_eval {|obj| obj == self } #=> true
# File 'vm_eval.c', line 2200
static VALUE rb_obj_instance_eval_internal(int argc, const VALUE *argv, VALUE self) { return specific_eval(argc, argv, self, TRUE, RB_PASS_CALLED_KEYWORDS); }
#instance_exec(arg...) {|var...| ... } ⇒ Object
Executes the given block within the context of the receiver (obj). In order to set the context, the variable self
is set to obj while the code is executing, giving the code access to obj’s instance variables. Arguments are passed as block parameters.
class KlassWithSecret
def initialize
@secret = 99
end
end
k = KlassWithSecret.new
k.instance_exec(5) {|x| @secret+x } #=> 104
# File 'vm_eval.c', line 2230
static VALUE rb_obj_instance_exec_internal(int argc, const VALUE *argv, VALUE self) { return yield_under(self, TRUE, argc, argv, RB_PASS_CALLED_KEYWORDS); }
#singleton_method_added(symbol) (private)
Invoked as a callback whenever a singleton method is added to the receiver.
module Chatty
def Chatty.singleton_method_added(id)
puts "Adding #{id.id2name}"
end
def self.one() end
def two() end
def Chatty.three() end
end
produces:
Adding singleton_method_added
Adding one
Adding three
#singleton_method_removed(symbol) (private)
Invoked as a callback whenever a singleton method is removed from the receiver.
module Chatty
def Chatty.singleton_method_removed(id)
puts "Removing #{id.id2name}"
end
def self.one() end
def two() end
def Chatty.three() end
class << self
remove_method :three
remove_method :one
end
end
produces:
Removing three
Removing one
#singleton_method_undefined(symbol) (private)
Invoked as a callback whenever a singleton method is undefined in the receiver.
module Chatty
def Chatty.singleton_method_undefined(id)
puts "Undefining #{id.id2name}"
end
def Chatty.one() end
class << self
undef_method(:one)
end
end
produces:
Undefining one