From: Jean-Hugues ROBERT <jean_hugues_robert@...>
Date: 2004-04-30T14:04:38+09:00
Subject: Re: coerce(), what protocol to implement it

At 08:39 30/04/2004 +0900, you wrote:
>Jean-Hugues ROBERT wrote:
>....
>>Google "ruby coerce" provided little help.
>>Thanks in advance,
>
>The coerce framework makes up for the lack of
>multiple dispatch aka "method overloading",
>whose lack can be a major nuisance when doing
>numerical work. You probably should study the
>source code of the standard libraries "complex"
>or "rational, if you want to get a feel for
>using this framework. Here is a scaled down
>example
>
>
>---
>class MyClass
>
>   def initialize(val)
>     @value = val
>   end
>
>   def coerce(other)
>     [MyClass.new(other),self]
>   end
>
>   def -(lhs)
>     if MyClass === lhs
>       MyClass::new(@value - lhs.value)
>     else
>       x,y = lhs.coerce(@value)
>       MyClass::new(x - y)
>     end
>   end
>
>   protected
>   attr_reader :value
>end
>
>p 1 - MyClass.new(5)
>p MyClass.new(5)  - 1
>
>
>require 'complex'
>
>z = Complex(1.0,1)
>
>p z - MyClass.new(5)
>p MyClass.new(5)  - z
>---
>#<MyClass:0x28a63e8 @value=-4>
>#<MyClass:0x28a6358 @value=4>
>#<MyClass:0x28955b8 @value=Complex(-4.0, 1)>
>#<MyClass:0x28954e0 @value=Complex(4.0, -1)>
>---
>/Christoph

Thanks a lot.

Looking for some example code I had had a look at
ruby/lib/ruby but there were so many files that I was
slightly lost.

Is there something like
   Class.implementers( meth)
that would return a list of all known classes that implement
some method ? It could not returned the classes that where
never required but it may help understand the protocols for
common methods that where designed to be redefined

Additionally, is there something like
   a_class.sources()
that would return an array of "positions" where source code
for a a_class was "loaded". It would return something similar
to what you get when an exception bombs at these positions.

If so, then
   Class.implementers( :coerce).each do | klass |
     p "coerce() is implemented by #{klass}, maybe in:"
     p a_class.sources.join( "\n")
   end
would list the files where there might be examples of how
to implement the :coerce method.

If I come up with a solution for this issue with Introspection,
I will share it here.

Thanks in advance,

BTW: With all the help I received I am well on my way to implement
a Reference class, like a Pointer but with some auto-dereferencing.
OTOH maybe I should investigate a "proxy" type of solution, like
the ones used by Drb or similar stuff.

Yours,

Jean-Hugues



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