From: Isaac Devine <isaac.devine@...>
Date: 2005-12-29T12:13:23+09:00
Subject: Re: [ANN] (Real) Primitive Ruby Generics support

On Wed, 28 Dec 2005 23:24:01 +0900
Florian Gro� <florgro@gmail.com> wrote:
> > I have been hacking away to create a simple library that adds
> > generics-like qualities to ruby. At the moment you can define
> > methods with type-matches, defaults if no match and different
> > number of argument matches.
> 
> Been there, done that:
> 
> http://ruby-contract.rubyforge.org/
> 
> New ideas are very welcome.
> 

Thanks! I've quickly looked at the ruby-doc for that. It's seems to
only be able to specific "contracts" for classes, with method
signatures as a subset. What my goal for generics is to be able to
choose what code to execute based on method/class parameter types.
ie.
converting :
def foo(arg)
 if arg.kind_of? String 
	puts "it is a string! reverse it! #{arg.reverse}"
 elsif arg.kind_of? Fixnum
	puts "Fixnum! double it! #{2*arg}"
 end
end

into:

generic_method :foo, String do |arg|
	puts "it is a string! reverse it! #{arg.reverse}"
end

generic_method :foo, Fixnum do |arg|
	puts "Fixnum! double it! #{2*arg}"
end

In the future I would like to be able to extend this to classes as
well. One implication of this we will be the ability to get rid of
"adapter" classes when joining heirachys. One example would be adding
support to reading from a String when a class can only read from a File.

ie.
generic_class :SomeClass, String do
	def getline
...
end

Another wish is for pattern matching:
  generic_method :foo, :a, :b :a do ...
where wherever :a occurs it must be the same type so:
  foo 4 "a" 4 passes
but 
  foo "a" 4 4 fails.

Looking at the rdoc some code in that could be very helpful - such as
Contact.adapt. 

thanks,
Isaac

P.S. I have an updated version which generates methods instead of
lookup + some extras. Nobody mind if I post it to the ml later(ie no
negative)?