UnboundMethod

Class

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 Methods

meth == other_meth → true or false
#

Two method objects are equal if they are bound to the same object and refer to the same method definition and their owners are the same class or module.

meth.arity → integer
#

Returns an indication of the number of arguments accepted by a method. Returns a nonnegative integer for methods that take a fixed number of arguments. For Ruby methods that take a variable number of arguments, returns -n-1, where n is the number of required arguments. Keyword arguments will be considered as a single additional argument, that argument being mandatory if any keyword argument is mandatory. For methods written in C, returns -1 if the call takes a variable number of arguments.

class C
  def one;    end
  def two(a); end
  def three(*a);  end
  def four(a, b); end
  def five(a, b, *c);    end
  def six(a, b, *c, &d); end
  def seven(a, b, x:0); end
  def eight(x:, y:); end
  def nine(x:, y:, **z); end
  def ten(*a, x:, y:); end
end
c = C.new
c.method(:one).arity     #=> 0
c.method(:two).arity     #=> 1
c.method(:three).arity   #=> -1
c.method(:four).arity    #=> 2
c.method(:five).arity    #=> -3
c.method(:six).arity     #=> -3
c.method(:seven).arity   #=> -3
c.method(:eight).arity   #=> 1
c.method(:nine).arity    #=> 1
c.method(:ten).arity     #=> -2

"cat".method(:size).arity      #=> 0
"cat".method(:replace).arity   #=> 1
"cat".method(:squeeze).arity   #=> -1
"cat".method(:count).arity     #=> -1

umeth.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

method.clone → new_method
#

Returns a clone of this method.

class A
  def foo
    return "bar"
  end
end

m = A.new.method(:foo)
m.call # => "bar"
n = m.clone.call # => "bar"

meth.eql?(other_meth) → true or false
#
An alias for ==

meth.hash → integer
#

Returns a hash value corresponding to the method object.

See also Object#hash.

meth.inspect → string
#

Returns a human-readable description of the underlying method.

"cat".method(:count).inspect   #=> "#<Method: String#count>"
(1..3).method(:map).inspect    #=> "#<Method: Range(Enumerable)#map>"

In the latter case, the method description includes the “owner” of the original method (Enumerable module, which is included into Range).

meth.name → symbol
#

Returns the name of the method.

meth.original_name → symbol
#

Returns the original name of the method.

class C
  def foo; end
  alias bar foo
end
C.instance_method(:bar).original_name # => :foo

meth.owner → class_or_module
#

Returns the class or module that defines the method. See also receiver.

(1..3).method(:map).owner #=> Enumerable

meth.parameters → array
#

Returns the parameter information of this method.

def foo(bar); end
method(:foo).parameters #=> [[:req, :bar]]

def foo(bar, baz, bat, &blk); end
method(:foo).parameters #=> [[:req, :bar], [:req, :baz], [:req, :bat], [:block, :blk]]

def foo(bar, *args); end
method(:foo).parameters #=> [[:req, :bar], [:rest, :args]]

def foo(bar, baz, *args, &blk); end
method(:foo).parameters #=> [[:req, :bar], [:req, :baz], [:rest, :args], [:block, :blk]]

meth.source_location → [String, Integer]
#

Returns the Ruby source filename and line number containing this method or nil if this method was not defined in Ruby (i.e. native).

meth.super_method → method
#

Returns a Method of superclass which would be called when super is used or nil if there is no method on superclass.

meth.to_s → string
#
An alias for inspect