From: Ryan Pavlik <rpav@...>
Date: 2003-07-19T13:32:04+09:00
Subject: Solution (Re: Default constructor)

On Sat, 19 Jul 2003 11:03:01 +0900
Pablo Lorenzzoni <spectra@debian.org> wrote:

> Hello!
> 
> class Klass
> 	attr_accessor :att1, :att2
> 	def initialize(att1, att2)
> 		@att1 = att1
> 		@att2 = att2
> 	end
> 	....
> end
> 
> Is it just me or the construction above is rather common? Is there such a 
> thing as a default cosntructor? Something that could turn that into
> 
<snip> 

Yes it is.  It's pretty easy to add, too, if you think Lisp.  This is a
little ugly... macros would make this WAY nicer... but here we go:

    def definit(*args, &block)
      s = ""
      args.each { |a| s << "@#{a.to_s} = #{a}\n" }
      arglist = args.join(', ')
    
      module_eval <<-END
          class << self; attr_reader :_post_init; end
          @_post_init = block
          def initialize(#{arglist})
              #{s}
              instance_eval &self.class._post_init if self.class._post_init
          end
      END
    end #m:definit

And of course, it wouldn't be complete without an example:

    class A
      attr_accessor :a, :b
    
      definit(:a, :b) {
        @a += 1
      }
    
      def show; p @a, @b; end
    end #c:A
    
    a = A.new(1, 2)
    a.show

This is why macros are cool.  Code that writes code is so extremely
useful. ;-)

(Note: I'm using 1.8 CVS, this may not work in 1.6.)

-- 
Ryan Pavlik <rpav@users.sf.net>

"Elfland? Mo' like pansyland." - 8BT