From: Christoph <chr_news@...>
Date: 2002-02-20T02:21:52+09:00
Subject: Re: Anonymous class support


<nobu.nokada@softhome.net> wrote in message
news:200202190622.g1J6MqX18863@sharui.nakada.kanuma.tochigi.jp...
> Hi,
>
> At Tue, 19 Feb 2002 10:33:31 +0900,
> David Corbin <dcorbin@imperitek.com> wrote:
> > I find Java anonymous classes to be very helpful when writing UnitTests,
> > because I can overide a method for "one time use" just to verify it gets
> > called correctly.
> >
> > I realize that I can write a new class that responds to whatever methods
> > I need.  But I'm talking about the syntactic convenience of  defining
> > the method as part of the the new call.
> >
> > Does Ruby have support for anything like this?
>
> As written already, you can use blocks, singleton methods, and
> anonymous class with Class.new like:
>
>   Class.new(superclass).class_eval do
>     def foo
>     end
>   end
>
> In 1.7, .class_eval isn't necessary.

Unfortunately you cannot use the ladder idiom within method bodies - for
example ..

----
class A
  def foo(&body)
    Class.new(type,&body)
  end
   def goo(&body)
     res = Class.new(type)
     res.class_eval &body  #  this works because &body is a string!
     res
   end
  #
end


anon =A.new.foo { Pointless = "okay" }
puts anon.const_get :Pointless    # => okay
# A.new.foo { def annoying_parse_error() end }


anon.new.goo { def okay(); puts "okay" end }.new.okay  # => okay
----


I was swearing to myself more than once about the latter parse error - i.e.
Matz
would make my day | week if he would do away with it in most situations ...


/Christoph