From: "John W. Long" <ng@...>
Date: 2003-11-08T11:29:11+09:00
Subject: Strong Typing (Re: Managing metadata about attribute types)

Ryan,

> > How can you prevent someone from using Strong Typing in the wrong
> > way?
>
> I don't believe this is the right question.

<snip>

> > How can you prevent someone from using Strong Typing in the wrong
> > way?

These two questions where meant to go together, but they are a little
confusing. What I meant was that a good api encourages people to use it in
the right way (it won't prevent them from doing something stupid).

My real question is more: Is there a better way to implement Strong Typing
so that people will not tend to use it in the wrong way?

I'm thinking of something along the lines of:

def my_method(a, b, c)
    expect a to implement this behavior #this seems more ruby like
    expect b to implement
    ...
end

This is essentially what you have written. However it is also easy to
implement it in a way more like statically typed languages:

def my_method(a, b, c)
    expect a is a String #this is more like basic, java, or c
    expect b is an Integer
    ...
end

Most of the reaction seems to be against the second option.

I could almost see this as a language feature:

def my_method(a implements StringBehavior, b implements IntegerBehavior, c)
    ...
end

Or even:

def my_method(a has DuckBehavior, b ...)
   ...
end

You could also implement this as an extension to Object:

def my_method(a, b, c)
    if a.has?(DuckBehavior)
        a.waddle
    else #waddle is preferred over trot
        a.trot if a.has?(HorseBehavior)
    end
end

Strange thoughts.
___________________
John Long
www.wiseheartdesign.com