Class: BasicObject

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

Overview

BasicObject is the parent class of all classes in Ruby. It's an explicit blank class.

BasicObject can be used for creating object hierarchies independent of Ruby's object hierarchy, proxy objects like the Delegator class, or other uses where namespace pollution from Ruby's methods and classes must be avoided.

To avoid polluting BasicObject for other users an appropriately named subclass of BasicObject should be created instead of directly modifying BasicObject:

class MyObjectSystem < BasicObject
end

BasicObject does not include Kernel (for methods like puts) and BasicObject is outside of the namespace of the standard library so common classes will not be found without a using a full class path.

A variety of strategies can be used to provide useful portions of the standard library to subclasses of BasicObject. A subclass could include Kernel to obtain puts, exit, etc. A custom Kernel-like module could be created and included or delegation can be used via #method_missing:

class MyObjectSystem < BasicObject
  DELEGATE = [:puts, :p]

  def method_missing(name, *args, &block)
    super unless DELEGATE.include? name
    ::Kernel.send(name, *args, &block)
  end

  def respond_to_missing?(name, include_private = false)
    DELGATE.include?(name) or super
  end
end

Access to classes and modules from the Ruby standard library can be obtained in a BasicObject subclass by referencing the desired constant from the root like ::File or ::Enumerator. Like #method_missing, #const_missing can be used to delegate constant lookup to Object:

class MyObjectSystem < BasicObject
  def self.const_missing(name)
    ::Object.const_get(name)
  end
end

Direct Known Subclasses

Object

Instance Method Summary collapse

Constructor Details

#new ⇒ Object

Returns a new BasicObject.




# File 'object.c'

/*
 * Not documented
 */

static VALUE
rb_obj_dummy(void)
{
    return Qnil;
}

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

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

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(methId)
    str = methId.id2name
    roman_to_int(str)
  end
end

r = Roman.new
r.iv      #=> 4
r.xxiii   #=> 23
r.mm      #=> 2000




# File 'vm_eval.c'

static VALUE
rb_method_missing(int argc, const VALUE *argv, VALUE obj)
{
    rb_thread_t *th = GET_THREAD();
    raise_method_missing(th, argc, argv, obj, th->method_missing_reason);
    return Qnil;        /* not reached */
}

Instance Method Details

#! ⇒ Object

Boolean negate.




# File 'object.c'

VALUE
rb_obj_not(VALUE obj)
{
    return RTEST(obj) ? Qfalse : Qtrue;
}

#!= ⇒ Object

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




# File 'object.c'

VALUE
rb_obj_not_equal(VALUE obj1, VALUE obj2)
{
    VALUE result = rb_funcall(obj1, id_eq, 1, obj2);
    return RTEST(result) ? Qfalse : Qtrue;
}

#==(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: it is used to determine object identity (that is, a.equal?(b) iff a is the same object as b).

The eql? method returns true if obj and anObject have the same value. Used by Hash to test members for equality. For objects of class Object, eql? is synonymous with ==. Subclasses normally continue this tradition, 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) 



# File 'object.c'

VALUE
rb_obj_equal(VALUE obj1, VALUE obj2)
{
    if (obj1 == obj2) return Qtrue;
    return Qfalse;
}

#__id__ ⇒ Object

call-seq:

obj.__id__       -> fixnum
obj.object_id    -> fixnum

Returns an integer identifier for obj. The same number will be returned on all calls to id for a given object, and no two active objects will share an id. Object#object_id is a different concept from the :name notation, which returns the symbol id of name. Replaces the deprecated Object#id.




# File 'gc.c'

/*
 *  call-seq:
 *     obj.hash    -> fixnum
 *
 *  Generates a <code>Fixnum</code> hash value for this object. This
 *  function must have the property that <code>a.eql?(b)</code> implies
 *  <code>a.hash == b.hash</code>. The hash value is used by class
 *  <code>Hash</code>. Any hash value that exceeds the capacity of a
 *  <code>Fixnum</code> will be truncated before being used.
 */

VALUE
rb_obj_id(VALUE obj)
{
/*
 *                32-bit VALUE space
 *          MSB ------------------------ LSB
 *  false   00000000000000000000000000000000
 *  true    00000000000000000000000000000010
 *  nil     00000000000000000000000000000100
 *  undef   00000000000000000000000000000110
 *  symbol  ssssssssssssssssssssssss00001110
 *  object  oooooooooooooooooooooooooooooo00        = 0 (mod sizeof(RVALUE))
 *  fixnum  fffffffffffffffffffffffffffffff1
 *
 *                    object_id space
 *                                       LSB
 *  false   00000000000000000000000000000000
 *  true    00000000000000000000000000000010
 *  nil     00000000000000000000000000000100
 *  undef   00000000000000000000000000000110
 *  symbol   000SSSSSSSSSSSSSSSSSSSSSSSSSSS0        S...S % A = 4 (S...S = s...s * A + 4)
 *  object   oooooooooooooooooooooooooooooo0        o...o % A = 0
 *  fixnum  fffffffffffffffffffffffffffffff1        bignum if required
 *
 *  where A = sizeof(RVALUE)/4
 *
 *  sizeof(RVALUE) is
 *  20 if 32-bit, double is 4-byte aligned
 *  24 if 32-bit, double is 8-byte aligned
 *  40 if 64-bit
 */
if (SYMBOL_P(obj)) {
    return (SYM2ID(obj) * sizeof(RVALUE) + (4 << 2)) | FIXNUM_FLAG;
}

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

Invokes the method identified by symbol, passing it any arguments specified. You can use __send__ if the name send clashes with an existing method in obj.

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

Overloads:




# File 'vm_eval.c'

VALUE
rb_f_send(int argc, VALUE *argv, VALUE recv)
{
    return send_internal(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: it is used to determine object identity (that is, a.equal?(b) iff a is the same object as b).

The eql? method returns true if obj and anObject have the same value. Used by Hash to test members for equality. For objects of class Object, eql? is synonymous with ==. Subclasses normally continue this tradition, 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) 



# File 'object.c'

VALUE
rb_obj_equal(VALUE obj1, VALUE obj2)
{
    if (obj1 == obj2) return Qtrue;
    return Qfalse;
}

#instance_eval(string[, filename [, lineno]]) ⇒ Object #instance_eval {|| ... } ⇒ 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. In the version of instance_eval that takes 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
end
k = KlassWithSecret.new
k.instance_eval { @secret }   #=> 99

Overloads:

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

    Returns:

  • #instance_eval {|| ... } ⇒ Object

    Yields:

    • ()

    Returns:




# File 'vm_eval.c'

VALUE
rb_obj_instance_eval(int argc, VALUE *argv, VALUE self)
{
VALUE klass;

if (SPECIAL_CONST_P(self)) {
klass = Qnil;
}

#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:




# File 'vm_eval.c'

VALUE
rb_obj_instance_exec(int argc, VALUE *argv, VALUE self)
{
VALUE klass;

if (SPECIAL_CONST_P(self)) {
klass = Qnil;
}

#singleton_method_added(symbol) ⇒ Object

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




# File 'object.c'

/*
 * Not documented
 */

static VALUE
rb_obj_dummy(void)
{
    return Qnil;
}

#singleton_method_removed(symbol) ⇒ Object

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




# File 'object.c'

/*
 * Not documented
 */

static VALUE
rb_obj_dummy(void)
{
    return Qnil;
}

#singleton_method_undefined(symbol) ⇒ Object

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




# File 'object.c'

/*
 * Not documented
 */

static VALUE
rb_obj_dummy(void)
{
    return Qnil;
}