From: Peter Cooper <peter@...>
Date: 2007-05-30T19:24:14+09:00
Subject: Re: Help with simple meta programming

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On 5/30/07, mario.lopes@gmail.com <mario.lopes@gmail.com> wrote:
>
> I want to change/create a new attr_accessor such that it calls a kind
> of proxy for retrieving the variable (which is not actually stored in
> the object itself but rather on the database).
>
> def variable
>   invoke_method(variable)
>   ...
> end
>
> def variable=(value)
>   invoke_method(variable, value)
>   ...
> end


There are a few ways to do this, and I'm surprised you haven't had a few
answers yet! So.. I'll provide some pointers in code. You will need to tidy
this up and structure it better, but it should at least demonstrate a
concept..

class Module
  # Why in Module and not Class? Because otherwise you couldn't use it
  # within module definitions.. only classes, whereas Module lets you cover
  # both..

  def attr_proxied_accessor(var)
    define_method(var) do
      # At this stage, we're defining the "x" method..
      10
    end

    define_method(:"#{var}=") do |v|
      # At this stage, we're defining the "x=" method..
    end
  end
end

class Something
  attr_proxied_accessor :x
end

puts Something.new.x

There's still some way to go, such as actually calling your proxy routines
and doing the "instance variable set/get", but it should at least crack the
biggest problem..? If you continue to get stuck, Googling around looking for
full code to attr_accessor provides a few techniques.

Cheers,
Peter Cooper
http://www.rubyinside.com/

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