From: ahoward <ahoward@...>
Date: 2003-06-19T00:35:12+09:00
Subject: Re: switching multiple interfaces of an object

On Wed, 18 Jun 2003, Mauricio [iso-8859-1] Fern�ndez wrote:

> Is this useful at all?

very.

> I thought of this as I was writing on the Adaptor pattern. I consider
> the above to be a "generalized" (dynamic) adaptor.

looks very cool.  i've done something similar (i think) using delegation:

~/eg/ruby > cat interface.rb
#!/usr/bin/env ruby
require 'delegate'

class Klass < SimpleDelegator

  def initialize
    @data = Data.new
    @a, @b, @c = [InterfaceA, InterfaceB, InterfaceC].map{|i| i.new @data}
    super @a
  end

  def interface= interface
    __setobj__(
      case interface.to_s
        when %r/^InterfaceA$/i
          @a
        when %r/^InterfaceB$/i
          @b
        when %r/^InterfaceC$/i
          @c
        else
          raise
      end
    )
  end

private
  class Data
    attr :data
    def initialize; @data = 42; end
  end
  class InterfaceA
    def initialize data; @data = data; end
    def meth; "InterfaceA: #{@data.data}"; end
  end
  class InterfaceB
    def initialize data; @data = data; end
    def meth; "InterfaceB: #{@data.data}"; end
  end
  class InterfaceC
    def initialize data; @data = data; end
    def meth; "InterfaceC: #{@data.data}"; end
  end
end

k = Klass.new
p k.meth

%w[InterfaceC InterfaceB InterfaceA].map{|i| k.interface = i and p k.meth}


~/eg/ruby > ruby interface.rb
"InterfaceA: 42"
"InterfaceC: 42"
"InterfaceB: 42"
"InterfaceA: 42"


care to comment on the relative merits/drawbacks of these approaches?  i really
do think something standard like this would be extremely useful.


-a
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