From: Robert Klemme <shortcutter@...>
Date: 2013-03-19T03:11:17+09:00
Subject: Re: Finding one's way with 'super' in define_method/alias_emthod

On Mon, Mar 18, 2013 at 5:50 PM, Marcin Rzeźnicki
<marcin.rzeznicki@gmail.com> wrote:
> Hi all!
> This is my first post here, so please don't yell at me too harshly :-)

Welcome to the wonderful world of Ruby!

> I have a little problem with 'super' keyword when it is used in
> define_method/alias_method. First, a little example:
>
>  class C
>    def greetings
>      p "Hello, #{caller.first}"
>    end
>    def curses
>      p "Damn you, #{caller.first}"
>    end
>  end
>
>  class D < C
>    def greetings
>      super
>    end
>    define_method :curses, instance_method(:greetings)
>  end
>
> [3] pry(main)> D.new.greetings
> "Hello, (pry):11:in `greetings'"
> => "Hello, (pry):11:in `greetings'"
> [4] pry(main)> D.new.curses
> "Hello, (pry):11:in `greetings'"
> => "Hello, (pry):11:in `greetings'"
>
> So, as you can see 'super' is bound, perhaps a little unexpectedly, to
> a method instance rather than to its call site.

Hmm, I'd still say it's the call site since the call site sits in
method D#greeting even though the method is also known as D#curse.

> You can see it clearly
> when inspecting the caller - in both cases it is 'greetings'. While
> this may seem logical and sound, it is quite troubling when you try to
> make a wrapper method around user-defined method doing metaprogramming
> tricks.

> Do you know any workaround? How can I overcome this problem and let
> super be bound correctly if used from aliased method? Thanks in
> advance for your opinions.

I am not sure what you expect should be called "bound correctly".
Basically what you did is you said D#curse should be D#greeting
(either via define_method as shown above or alias).  That means, D's
method #curse behaves like D's #greeting and hence ultimately invokes
C#greeting and not C#curse.

Btw, somehow your chain example seems incomplete: is #chain a method
defined in Module?  What about method names?  I would have expected
the chained method name to be given as argument.

I once coded something together for wrapping methods - you may find it
in the archives.  I am not sure though that I still have the code
elsewhere...  I only found this one:
https://gist.github.com/rklemme/3002732 but that's not the one I mean.

Kind regards

robert


-- 
remember.guy do |as, often| as.you_can - without end
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