class BasicObject - Documentation for Ruby 3.5 (original) (raw)

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.superclass

BasicObject is the only class that has no parent:

BasicObject.superclass

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 as puts, 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 or false.
• !=: 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.

Public Class Methods

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#define rb_obj_initialize rb_obj_dummy0

Returns a new BasicObject.

Public Instance Methods

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VALUE rb_obj_not(VALUE obj) { return RBOOL(!RTEST(obj)); }

Boolean negate.

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VALUE rb_obj_not_equal(VALUE obj1, VALUE obj2) { VALUE result = rb_funcall(obj1, id_eq, 1, obj2); return rb_obj_not(result); }

Returns true if two objects are not-equal, otherwise false.

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VALUE rb_obj_equal(VALUE obj1, VALUE obj2) { return RBOOL(obj1 == obj2); }

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
obj.equal? other
obj.equal? obj

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
1.eql? 1.0

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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, object_id); }

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
(21 * 2).object_id == (21 * 2).object_id
"hello".object_id == "hello".object_id
"hi".freeze.object_id == "hi".freeze.object_id

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VALUE rb_f_send(int argc, VALUE *argv, VALUE recv) { return send_internal_kw(argc, argv, recv, CALL_FCALL); }

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"

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
obj.equal? other
obj.equal? obj

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
1.eql? 1.0

Alias for: ==

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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); }

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 }
k.instance_eval { the_secret }
k.instance_eval {|obj| obj == self }

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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); }

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 }

Private Instance Methods

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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); }

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
r.xxiii
r.mm
r.foo

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#define rb_obj_singleton_method_added rb_obj_dummy1

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

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#define rb_obj_singleton_method_removed rb_obj_dummy1

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

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#define rb_obj_singleton_method_undefined rb_obj_dummy1

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