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