From: Richard Kilmer <rich@...>
Date: 2004-06-08T10:40:42+09:00
Subject: Re: How to ducktype a Hash?




On 6/7/04 7:37 PM, "Jim Weirich" <jim@weirichhouse.org> wrote:

>>>> Maybe:
>>>> 
>>>>  f<Array>['rich']
>>>>  f.<Person>[firstname]
>>>> 
>>>> It's ugly enough to discourage its use, but it also calls
>>> to mind the
> 
> I missed what this syntax (and the other proposals) is supposed to
> accomplish and the threading in this topic thread is wonky enough so
> that I can't find the parent messages.  Could someone fill me in.

The key is expressing that a method you are defining is semantically
equivalent to a method in another class/module.

Contrived example:

class NameList
  def initialize
    @list = []
  end
  def first_name
    @list.first
  end
end

class Person
  attr_reader :first_name
end

class Robot
  def <Person>first_name
    @first_name
  end
end

This says that Robot's first_name method is semantically equivalent to
Person's first_name method (with all that that semantics carries with
it...which may be a lot, and may not be much).  You can "cast" the method
call to an instance:

r = Robot.new

Like this:

r.<Person>first_name

But if you did this:

r.<NameList>first_name

It would raise an exception.

And perhaps extend respond_to? to include an (optional) Class/Module name.

r.respond_to?(:first_name) => true
r.respond_to?(:first_name, Person) => true
r.respond_to?(:first_name, NameList) => false

All this is optional of course.  Gavin proposed using <...>, I had
originally used {...}

-rich