From: patrick-may@... (Patrick May)
Date: 2002-09-13T08:41:33+09:00
Subject: Re: not grasping the method overloading/multi-dispatch thing

Philipp Meier <meier@meisterbohne.de> wrote in message news:<20020912131150.GA25625@o-matic.net>...
> class Foo
> 	def meth(Integer i, Integer j) 
> 		i.to s + j.to s
> 	end
> 
> 	def meth(Object o1, Object o2) 
> 		o1+o2
> 	end
> end

what is wrong with something like:

class Foo
    def meth( i, j )
        i.to_s + j.to_s
    end
end

> Which is reasonably shorted and easier to understand. I see a need for
> this as I find myself often manually dispatching to methods by the type
> of an argument.

Is this a good example of the types of dispatches you often do?

Dispatching on type smells like there is a need for some polymorphic
method.  For example:

def description( build_target )
    case build_target.class
    when Compile
        "compile libraries"
    when InstallDependencies
        "install dependencies"
    else


        "unknown target"
    end
end

(I doubt that code in the wild would be this obvious)

To me, the point of OO programming is to have one conditional that
picks the type.  If you find conditionals on type downstream from your
factories, then I think it's a sign of methods that should be on the
classes, i.e. Compile.description, InstallDependencies.description,
etc.

Another point -- it is possible to dispatch on type in Ruby, just not
easy.  Proposed multimethods wouldn't allow you write new
functionality, but it would make it easier to have downstream
conditionals on types.

In my opinion, I don't think this is a good idea.  This kind of code
is a smell to me, and I'd rather keep it real smelly to encourage me
to clean it up.  Throwing some syntax deoderant (sp) would just make
it harder for me to see code begging me to midwife some new methods
:-)

~ Patrick