From: Igor Pirnovar <lists@...>
Date: 2012-11-04T06:20:59+09:00
Subject: Re: why does UnboundMethod need to remember the class it was retrieved from (not merely owner)?

Mean L. wrote in post #1082655:

> This does not answer the question.

How comes? It is the rule, that you can not bind a method to anything
but to the object that is an instance of a subclass of the class of the
original object. You are trying to bind it to an instance of its parent
or the superclass.

See, if you make a subclass 'A' of your 'Sub', all works as spelled out
by the Ruby rules, however if you try to bind to the object whose class
is the parent of your 'Sub' you get the error, which BTW, spells out
precisely what you missed here:

  class Base; def foo; puts "in Base"; end; end
  class Sub < Base; end
  class A < Sub; end

  base_foo = Base.instance_method :foo
  sub_foo = Sub.instance_method :foo

  base_foo.bind(Base.new).call #=> "in Base"
  sub_foo.bind(A.new).call     #=> "in Base"

  sub_foo.bind(Base.new).call  #=> ./b-u_test.rb:24:in `bind': \
           bind argument must be an instance \
           of Sub (TypeError) \
           from ./b-u_test.rb:24:in `<main>'

Regards, igor

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