From: David Alan Black <dblack@...>
Date: 2001-11-03T08:44:28+09:00
Subject: [ruby-talk:24233] Re: Too much eval evil? (tell me why I shouldn't do this)

Hello --

On Sat, 3 Nov 2001, Thomas Gandy wrote:

> I've been doodling with Ruby (experimenting with it in order to figure
> out what it's capable of) like a kid with crayons... ;-)
>
> So here I present some thoughts and I request a critique.
>
> Let's say I've got a string which has some ruby variables in it and I
> want each of those variables to take on a range of values and then I
> want to evaluate that string given every combination of those values
> (a cartesian product).  And of course I want to be able to use this
> with a variable number of varying variables, so my cartesian product
> function has to work given any number of variables.
>
> Since you get a cartesian product of a fixed number of arrays by
> doing:
> #say we have three arrays:
> a_ary.each { |a|
>    b_ary.each { |b|
>       c_ary.each { |c|
>          puts "a=#{a}, b=#{b}, c=#{c}
>       }
>    }
> }
>
> That's all well and good if you know up front that you'll only have
> three arrays to deals with, but if you don't....  My idea was to
> create the cartesian product function dynamically and to an
> instance_eval of it.  I present the code below.  Please let me know if
> this is a crazy idea or not and also present alternatives:

I don't have a full-blown alternative, but just a suggestion: have you
looked at the Matrix class?  (matrix.rb in the Ruby distribution) I'm
not sure whether it is relevant, but you might have a look.


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav