From: Sean O'Dell <sean@...>
Date: 2004-06-08T12:36:28+09:00
Subject: Re: Interfaces and semantics (or, how to hashpipe a duck)

On Monday 07 June 2004 20:13, Hal Fulton wrote:
> Semantics, James Thurber notwithstanding, is not a town in Ohio.
>
> I think when Rich says "semantics" he means something that can't
> really be checked by a machine -- the "purpose or function," as it
> were.
>
> I do sometimes wish there were a way to detect semantics -- but the
> best we could do is simply remove the problem a step further.

Here's what I'm working on right now for my own purposes.  I've already 
applied for a RubyForge project so if others find this useful, they can use 
it too.  Take a look:

# first class defines the interface
class MyClass
  def method1(a, b, c)
  end

  def method2(a, b, c = nil)
  end

  define_interface(:my_interface, :method1, :method2)
end

# of course it has its own interface
a = MyClass.new
a.has_interface?(:my_interface) => true

# second class simply declares that it implements the interface
class UnrelatedClass
  declare_interface(:my_interface)

  def method1(a, b, c)
  end

  def method2(a, b, c = nil)
  end
end

# it also implements the interface
a = UnrelatedClass.new
a.has_interface?(:my_interface) => true

# the third class declares the interface
# but changes one of the methods' parameters to have no default
class NoncompliantClass
  declare_interface(:my_interface)

  def method1(a, b, c)
  end

  def method2(a, b, c)
  end
end

# because of the method change, it does not implement the interface
a = NoncompliantClass.new
a.has_interface?(:my_interface) => false



I'm writing a little lib in C to do this right now.  I'm mostly done.  I am 
fighting with the Ruby C API's class variable access, otherwise I'd be 
finished.

	Sean O'Dell