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Class: UnboundMethod

Relationships & Source Files
Inherits: Object
Defined in: proc.c,
proc.c

Overview

Ruby supports two forms of objectified methods. ::Class Method is used to represent methods that are associated with a particular object: these method objects are bound to that object. Bound method objects for an object can be created using Object#method.

Ruby also supports unbound methods; methods objects that are not associated with a particular object. These can be created either by calling Module#instance_method or by calling #unbind on a bound method object. The result of both of these is an UnboundMethod object.

Unbound methods can only be called after they are bound to an object. That object must be a kind_of? the method's original class.

class Square
  def area
    @side * @side
  end
  def initialize(side)
    @side = side
  end
end

area_un = Square.instance_method(:area)

s = Square.new(12)
area = area_un.bind(s)
area.call   #=> 144

Unbound methods are a reference to the method at the time it was objectified: subsequent changes to the underlying class will not affect the unbound method.

class Test
  def test
    :original
  end
end
um = Test.instance_method(:test)
class Test
  def test
    :modified
  end
end
t = Test.new
t.test            #=> :modified
um.bind(t).call   #=> :original

Instance Method Summary

Instance Method Details

#==(other_meth) ⇒ Boolean Also known as: #eql?

Alias for Method#==.

#arityInteger

Alias for Method#arity.

#bind(obj) ⇒ method

Bind umeth to obj. If Klass was the class from which umeth was obtained, obj.kind_of?(Klass) must be true.

class A
  def test
    puts "In test, class = #{self.class}"
  end
end
class B < A
end
class C < B
end

um = B.instance_method(:test)
bm = um.bind(C.new)
bm.call
bm = um.bind(B.new)
bm.call
bm = um.bind(A.new)
bm.call

produces:

In test, class = C
In test, class = B
prog.rb:16:in `bind': bind argument must be an instance of B (TypeError)
 from prog.rb:16
[ GitHub ]

  
# File 'proc.c', line 2344

static VALUE
umethod_bind(VALUE method, VALUE recv)
{
    struct METHOD *data, *bound;
    VALUE methclass, klass;

    TypedData_Get_Struct(method, struct METHOD, &method_data_type, data);

    methclass = data->me->owner;

    if (!RB_TYPE_P(methclass, T_MODULE) &&
	methclass != CLASS_OF(recv) && !rb_obj_is_kind_of(recv, methclass)) {
	if (FL_TEST(methclass, FL_SINGLETON)) {
	    rb_raise(rb_eTypeError,
		     "singleton method called for a different object");
	}
	else {
	    rb_raise(rb_eTypeError, "bind argument must be an instance of % "PRIsVALUE,
		     methclass);
	}
    }

    klass  = CLASS_OF(recv);

    method = TypedData_Make_Struct(rb_cMethod, struct METHOD, &method_data_type, bound);
    RB_OBJ_WRITE(method, &bound->recv, recv);
    RB_OBJ_WRITE(method, &bound->klass, data->klass);
    RB_OBJ_WRITE(method, &bound->me, rb_method_entry_clone(data->me));

    if (RB_TYPE_P(bound->me->owner, T_MODULE)) {
	VALUE ic = rb_class_search_ancestor(klass, bound->me->owner);
	if (ic) {
	    klass = ic;
	}
	else {
	    klass = rb_include_class_new(methclass, klass);
	}
	RB_OBJ_WRITE(method, &bound->me, rb_method_entry_complement_defined_class(bound->me, bound->me->called_id, klass));
    }

    return method;
}

#cloneMethod

Alias for Method#clone.

#==(other_meth) ⇒ Boolean #eql?(other_meth) ⇒ Boolean

Alias for #==.

#hashInteger

Alias for Method#hash.

#to_sString

Alias for Method#inspect.

#nameSymbol

Alias for Method#name.

#original_nameSymbol

#ownerclass_or_module

Alias for Method#owner.

#parametersArray

Alias for Method#parameters.

#source_locationArray, Integer

#super_methodMethod

Alias for Method#super_method.

#to_s

Alias for Method#inspect.

[ GitHub ]