From: Niklas Frykholm <niklas@...>
Date: 2001-11-11T20:14:10+09:00
Subject: [ruby-talk:24872] Re: Help needed on subclassing

[Robert Feldt]:
> Its late here in Sweden (actually early, but anyway... ;-)) and I cant
> find an elegant way to from class M subclass class T so that in
> the subclass some (but not all) of the arguments for T.new are specified.
> 
> Example:
>  T is class with T.new(a,b,c)
>  M.[] needs to return a subclass of T (lets call it S) so that calls
>        S.new(c) are translated to T.new(am,bm,c).

What about this?

    class T
      def initialize(a,b,c)
        puts "T #{a} #{b} #{c}"
      end
    end

    class M
      def [](x)
        s = Class.new(T)
        class << s
          def new(c)
            T.new(1,2,c)
          end
        end
        return s
      end
    end

Or if you don't need S to be a real class, you could do:

    class T
      def initialize(a,b,c)
        puts "T #{a} #{b} #{c}"
      end
    end

    class SMeta
      def initialize(am, bm)
        @am, @bm = am, bm
      end

      def new(c)
        T.new(@am, @bm, c)
      end
    end

    class M
      def [](x)
        SMeta.new(1,2)
      end
    end

// Niklas