From: Thomas <sanobast-2005a@...>
Date: 2005-05-23T17:44:13+09:00
Subject: Re: Uniform vector class, inheriting from Array: How to make sure that methods return a Vector and not an Array?

> I'm quite shure you don't need to do what you are doing, because this
> violates duck typing

Thank you very much for pointing out how to use method_missing here.

BTW I don't think that it "violates" duck typing. The idea is to have a 
collection type class with "entrance rules" that can guarantee that 
every single element complies with some sort of standard/interface/rule 
set/constraints/contracts ... Using kind_of? is only one possible 
constraint here. Another one could be respond_to?(:quack). On the long 
run, I would like it to look/feel like this:

class QuackQuack < UniformArray
	add_contstraint lambda {|e| e.respond_to?(:quack)}
end

class ArmyOfDucks < UniformArray
	add_contstraint lambda {|e| e.kind_of?(Duck)}
end

class FlockOfDucks < UniformArray
	add_contstraint lambda {|e| e.kind_of?(Duck)}
	permit nil         # There may be nil values
	allow :nested      # The array may be nested
end

d = UniformArray.new
d.add_contstraint lambda {|e| e.kind_of?(Numeric) and e >= 0 and e <= 10}
d.add_handler lambda {|e| e > 10 ? 10 : 0}

etc.

I don't think this is incompatible with duck typing. It's just some sort 
of specialized collection type of class.

Cheers,
Thomas.