Class: BasicObject

Inherits:
Qnil show all
Defined in:
object.c,
class.c,
object.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 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.

Direct Known Subclasses

Object, Ractor::MovedObject

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Object (private)

call-seq:

BasicObject.new

Returns a new BasicObject.

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#method_missing(symbol[, *args]) ⇒ Object (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



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# 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.

Returns:

  • (Boolean) 


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# 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.

Returns:

  • (Boolean) 


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# 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

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

Overloads:

  • #==(other) ⇒ Boolean

    Returns:

    • (Boolean)
  • #equal?(other) ⇒ Boolean

    Returns:

    • (Boolean)
  • #eql?(other) ⇒ Boolean

    Returns:

    • (Boolean) 


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# File 'object.c', line 245

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

#__id__ ⇒ Object

call-seq:

obj.__id__       -> integer
obj.object_id    -> integer

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



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# File 'gc.c', line 1898

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);
}

#send(symbol[, args...]) ⇒ Object #__send__(symbol[, args...]) ⇒ Object #send(string[, args...]) ⇒ Object #__send__(string[, args...]) ⇒ Object

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+.
<code>__send__</code> is safer than +send+
when _obj_ has the same method name like <code>Socket</code>.
See also <code>public_send</code>.

   class Klass
     def hello(*args)
       "Hello " + args.join(' ')
     end
   end
   k = Klass.new
   k.send :hello, "gentle", "readers"   #=> "Hello gentle readers"

Overloads:



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# 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

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

Overloads:

  • #==(other) ⇒ Boolean

    Returns:

    • (Boolean)
  • #equal?(other) ⇒ Boolean

    Returns:

    • (Boolean)
  • #eql?(other) ⇒ Boolean

    Returns:

    • (Boolean) 


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# File 'object.c', line 245

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

#instance_eval(string[, filename [, lineno]]) ⇒ Object #instance_eval {|obj| ... } ⇒ Object

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

Overloads:

  • #instance_eval(string[, filename [, lineno]]) ⇒ Object

    Returns:

  • #instance_eval {|obj| ... } ⇒ Object

    Yields:

    • (obj)

    Returns:



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# File 'vm_eval.c', line 2291

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

Yields:

  • (var...)

Returns:



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# File 'vm_eval.c', line 2321

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 ⇒ Object (private)

call-seq:

   singleton_method_added(symbol)

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

<em>produces:</em>

   Adding singleton_method_added
   Adding one
   Adding three

#singleton_method_removed ⇒ Object (private)

call-seq:

   singleton_method_removed(symbol)

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

<em>produces:</em>

   Removing three
   Removing one

#singleton_method_undefined ⇒ Object (private)

call-seq:

   singleton_method_undefined(symbol)

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

<em>produces:</em>

   Undefining one