From: Ryan Leavengood <mrcode@...>
Date: 2005-04-30T03:49:08+09:00
Subject: Re: ruby static typing

Lyndon Samson wrote:
>
> Although they were GUI specific, Remember VBX/OCX, how sweet it was
> that you could drop in 3rd party functionality into a MS IDE and the
> IDE would immediatly know what the interface to be presented to the
> programmer was.
>
> Imagine trying to do the same in Ruby or another softly typed
> language, A whole lot of framework code would need to be written and
> maintained ( human written unit tests vs compiler enforced type
> checking ).

This is probably a naive implementation of what you described above (and
maybe I've misinterpreted you), but it still isn't all that complicated:

class Class
  def exposed_methods
    @exposed_methods ||= []
  end

  def attr_exposed(*method_symbols)
    (@exposed_methods ||= []).concat method_symbols
  end
end

class MyComponent
  attr_exposed :do_this, :do_that

  def do_this
    "do this!"
  end

  def do_that
    "do that!"
  end
end

class ComponentUser
  def ComponentUser::show_component_methods(component_class)
    puts "Exposed methods for #{component_class.name}:"
    obj = component_class.new
    component_class.exposed_methods.each do |m|
      arity = obj.method(m).arity
      puts "-  #{m}(#{arity >= 0 ? arity : 'variable number of'} arguments)"
    end
  end
end

class String
  attr_exposed :[], :slice, :each_byte
end

if $0 == __FILE__
  ComponentUser.show_component_methods(MyComponent)
  ComponentUser.show_component_methods(String)
  ComponentUser.show_component_methods(Array)
end

This way you can limit clients to what methods they can use based on the
exposed_methods. Of course the clients need to play along nicely, which
Ruby  can't necessarily force them to do. But this begs the question,
isn't Class#instance_methods(false) essentially the same as this
exposed_methods in most cases?

Of course after writing this I realized you still don't know what the
arguments mean. But that is what ri is for. Plus even with Java or other
component frameworks you still need some information external to the
component to learn how to use it, even if you know what the static types
of the arguments are.

The results from the above exposed_methods call could be linked with ri in
a component system to ease this. Hmmm, not a bad idea...

Ryan