From: Daniel Schierbeck <daniel.schierbeck@...>
Date: 2006-04-02T00:53:44+09:00
Subject: [Facets] Add a Module#attr_validator method

I couldn't find a Facets mailing list, and I know the developers use 
this list, so therefore I send my proposal here.

I'd like to see the addition of an attribute validator, i.e. a setter 
that checks to see if a block returns true when called with the new 
value as its only argument. Without further ado, I hereby present 
Module#attr_validator:

   class Module
     def attr_validator(*symbols, &validator)
       symbols.each do |symbol|
         define_method "#{symbol}=" do |val|
           unless validator.call(val)
             raise ArgumentError, "Invalid value provided for #{symbol}"
           end
           instance_variable_set("@#{symbol}", val)
         end
       end
     end
   end

Use it, change it, polish it - it's yours.


Cheers,
Daniel Schierbeck