From: "Mean L." <lists@...>
Date: 2012-11-04T12:06:43+09:00
Subject: Re: why does UnboundMethod need to remember the class it was retrieved from (not merely owner)?

Igor Pirnovar wrote in post #1082696:
> Mean L. wrote in post #1082692:
>
>> "why does UnboundMethod need to remember the class it was retrieved
>> from (not merely owner)?"
>
> Because, the UnboundMethod can not be bound to an object that is not
> instantiated as subclass of the class of the owner of the unbound
> method. That is the requirement if you wish to bound it, period!

I thought you at least understood the rule as it is, since you kept 
referring to it over and over. Let's examine what you posted:

"can not be bound to an object that is not" -- cancelling the double 
negative gives us:

"the UnboundMethod can only be bound to an object that is an instance of 
a subclass of the owner class"

This is false on two separate counts:

1. It's not the owner that matters, but the class via which you retrieve 
the method (the one you call instance_method on), they are not the same.

class Base; def foo; end end
class Sub < Base; end
class SubSub < Sub; end

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

sub_sub_foo.bind(Sub.new).call

In the above example, the owner of sub_sub_foo (sub_sub_foo.owner) is 
Base, Sub.new is an instance of Sub which is a subclass of Base, which 
satisfies your misconception/misstatement of the current rule.

2. even if we replace in you misstated rule, "owner" by "class on which 
instance_method was called to retrieve the method", it is still wrong 
because it refers to subclass, instead of subclass or same class.

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