Forum: Ruby Help with simple meta programming

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(Guest)
on 2007-05-30 11:45
(Received via mailing list)
Hi,

This is a basic question of meta-programming with Ruby, which I'm
still getting familiar with.

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

So, I catch the method name which should correspond to the variable
(except for the set method, which includes an extra '=') and pass it
to another function.

Any hints on how to get it done the right way? Thanks!

Cheers,

Mário
Peter C. (Guest)
on 2007-05-30 14:25
(Received via mailing list)
On 5/30/07, removed_email_address@domain.invalid 
<removed_email_address@domain.invalid> wrote:
> 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 C.
http://www.rubyinside.com/
Robert D. (Guest)
on 2007-05-30 15:40
(Received via mailing list)
On 5/30/07, removed_email_address@domain.invalid 
<removed_email_address@domain.invalid> wrote:
>   invoke_method(variable)
> to another function.
>
> Any hints on how to get it done the right way? Thanks!
>
> Cheers,
>
> Mário
>
>
>
Maybe you would like to have a look at my personal favorite of all
Ruby Q.zes(*) (well that is of course save my own - just kidding-
there are lots of close seconds BTW):
http://rubyquiz.com/quiz67.html
I am quite sure that this should cover your needs.

Cheers
Robert

(*) although I miserably failed to find a solution (at that time).
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