From: E S <eero.saynatkari@...>
Date: 2005-01-26T07:51:57+09:00
Subject: Re: Injecting methods from one class into another.

> L�hett�j�: "George  Moschovitis" <george.moschovitis@gmail.com>
> Aihe: Re: Injecting methods from one class into another.
> 
> > I do not think what you want has anything to do with 'duck typing'.
> 
> Of course it has. Have a look at the following example:
>
> class C1
> attr_accessor :a
> 
> def a1
> puts @a
> end
> 
> def a2
> puts 'hello'
> end
> end
> 
> class C2
> attr_accessor :a
> end
> 
> So for method C1#a1 the class C2 'quacks like a duck' (ie, it has the
> attribute @a)
> 
> So in 'duck typing' spirit, it should be possible to do:
> 
> c = C2.new
> 
> m = C1.instance_method(:a1)
> m.bind(c)
> 
> c.a1
> 
> however Ruby raises a TypeError :(

You're forgetting something. It's not "If it quacks...", it's 
"If it quacks... and if it walks...". The gist is that as long as
an object has *all* of the (required) characteristics of a type, the 
object can be treated as a specimen of that type.

As an animal analogy regarding 'injecting' methods, tearing off the 
wings of a duck and gluing them to a pig doesn't mean the pig can fly.

> Can anyone give me an example, where this #bind method is usefull? I
> mean,  you can only bind a Method back to an object of the original
> method's Class or a Subclass. But such an object allready has this
> method, so whats the point?
> Am I missing something here?
> 
> regards, 
> George

E