Help with simple meta programming

Ruby
1

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

2

On 5/30/07, [email protected] [email protected] 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.

3

On 5/30/07, [email protected] [email protected] 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).