From: Paul Lutus <nospam@...>
Date: 2006-12-12T06:25:05+09:00
Subject: Re: best way to dynamically create new instance methods

Dan Tenenbaum wrote:


> That seems pretty simple but I have run into all sorts of problems with
> various ways of doing it. Rather than recount all those ways and why
> they didn't work, I instead present the minimal example of the problem I
> am trying to solve and hope that someone can solve it.

Rather than try to sort out a way to create methods on the fly, perhaps it
would be better if you were to explain what you are trying to do ... what
problem does this approach solve?

There are any number of ways to produce results for given input data, and
creating new methods for a class at runtime is not necessarily the most
efficient way to accomplish your goal.

What I am saying is you are now struggling to solve, not the original
problem your program is meant to solve, but the problems created by your
solution.

One possible alternative is a hash with keys consisting of identifying
labels, and values consisting of lambdas that can produce various kinds of
results. The lambdas could easily stand in for your custom methods, and
this approach might end up being easier to implement.

Example:

----------------------------------------

#!/usr/bin/ruby -w

hash = {
   "+" => lambda { |x,y| x + y },
   "-" => lambda { |x,y| x - y },
   "*" => lambda { |x,y| x * y },
   "/" => lambda { |x,y| x / y },
}

puts hash["/"].call(1.0,3.0)

----------------------------------------

Output:

0.333333333333333

Depending on what you are trying to do, this might be easier to use and
might be faster as well, especially if you take your development time into
account. 

-- 
Paul Lutus
http://www.arachnoid.com