From: Dave Thomas <Dave@...>
Date: 2001-05-21T05:05:27+09:00
Subject: [ruby-talk:15434] A proto-RCR: making def and class rvalues


Currently, method and class definitions return values, but:

1. It's hard to use these values, as the syntax doesn't allow a method
   or class definition as an rvalue (so you have to get to them via
   'eval'), and

2. The value of these statements isn't too useful. Method definitions
   return 'nil', and class definitions return the value of the last
   executed statement in the definition.


I'm wondering about the following set of changes:

1. Allow class and method definitions to appear as rvalues

2. Have class definitions always return the newly defined class.

3. Have method definitions return an UnboundMethod object
   corresponding to the method just defined.

4. Add methods to UnboundMethod to return the name and name as symbol
   of the method.

5. Alter the functions and statements that currently accept a method
   name or symbol to also accept an UnboundMethod object.


The motivation for all this is that it would make programming various
extensions in the Ruby language far more natural. For example, there
was recently a thread on synchronized methods. You could write
something like:

    class Rubble
      def fred
        #...
      end
      synchronized :fred
    end

Say instead that 'def' returned the method object, and you could use
a def as an rvalue (say as the parameter to a method). Then you could
write

    class Rubble
      synchronized def fred
        #...
      end
    end

The method gets defined, the UnmoundMethod object gets passed to the
method 'synchronized' which then does its magical wrapping.

You could also use this at the class level:

   synchronized class Rubble
      # ...

   singleton class Bedrock


   persistent class Quarry


and so on.


Does this have merit? Are there any gotchas I'm missing?


Dave