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. 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)
    DELEGATE.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

#initializeObject (private)

Not documented


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# File 'object.c', line 828

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

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

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# File 'vm_eval.c', line 621

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);
    UNREACHABLE;
}

Instance Method Details

#!Object

Boolean negate.


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# File 'object.c', line 150

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

#!=Object

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


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# File 'object.c', line 163

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 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

a == other      #=> true
a.equal? other  #=> false
a.equal? a      #=> 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 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 108

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

#hashFixnum

Generates a Fixnum hash value for this object.

This function must have the property that a.eql?(b) implies a.hash == b.hash.

The hash value is used by Hash class.

Any hash value that exceeds the capacity of a Fixnum will be truncated before being used.

Returns:


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# File 'gc.c', line 1688

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;
    }
    else if (FLONUM_P(obj)) {
#if SIZEOF_LONG == SIZEOF_VOIDP
	return LONG2NUM((SIGNED_VALUE)obj);
#else
	return LL2NUM((SIGNED_VALUE)obj);
#endif
    }
    else if (SPECIAL_CONST_P(obj)) {
	return LONG2NUM((SIGNED_VALUE)obj);
    }
    return nonspecial_obj_id(obj);
}

#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:


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# File 'vm_eval.c', line 882

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 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

a == other      #=> true
a.equal? other  #=> false
a.equal? a      #=> 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 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)

Returns:

  • (Boolean)

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# File 'object.c', line 108

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:


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# File 'vm_eval.c', line 1572

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

    if (SPECIAL_CONST_P(self)) {
	klass = rb_special_singleton_class(self);
    }
    else {
	klass = rb_singleton_class(self);
    }
    return specific_eval(argc, argv, klass, self);
}

#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 1604

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

    if (SPECIAL_CONST_P(self)) {
	klass = rb_special_singleton_class(self);
    }
    else {
	klass = rb_singleton_class(self);
    }
    return yield_under(klass, self, rb_ary_new4(argc, argv));
}

#singleton_method_addedObject (private)

Not documented


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# File 'object.c', line 828

static VALUE
rb_obj_dummy(void)
{
    return Qnil;
}

#singleton_method_removedObject (private)

Not documented


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# File 'object.c', line 828

static VALUE
rb_obj_dummy(void)
{
    return Qnil;
}

#singleton_method_undefinedObject (private)

Not documented


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# File 'object.c', line 828

static VALUE
rb_obj_dummy(void)
{
    return Qnil;
}