From: ptkwt@...1.aracnet.com (Phil Tomson)
Date: 2001-12-11T07:40:32+09:00
Subject: [ruby-talk:28145] Re: The benefits of dynamic typing?

In article <3C153282.9000309@vt.edu>, Roy Patrick Tan  <rtan@vt.edu> wrote:
>Phil Tomson wrote:
>
>> then if I, or a user of these 
>> classes decide that they want a different kind of runnable object that 
>> performs a differnt function when 'run' is called, all they 
>> have to do is define another class of their own and make sure it's objects 
>> respond to 'run'.
>
>
>This is somehow disturbing to me. "Run" is kind of ambiguous, and might 
>behave differently for different objects, whereas the caller of the 
>method expects "run" to behave in a certain way, shouldn't a 
>compiler/interpreter make sure that  it *does* behave that way (ie check 
>the contract)?
>

But if the caller object "expects 'run' to behave in a certain way" 
doesn't that imply that encapsulation is broken in the system?


Isn't the contract the method signature (the messages an object will 
respond to) of the runnable object?  In my system (and this example is 
based on a real world framework I've implemented) as long as the object 
passed defines a 'run' method, it is runnable.  The object receiving the 
runnable object (which then invokes the runnable object's 'run' method) 
doesn't have any concerns about what invoking 'runnableObj.run' will do.
This, in fact, made my framework very simple.  Let me explain: I was tryng 
to distribute tasks to multiple clients using dRuby.  And I also wanted 
users of the framework to be able to create their own runnable objects 
(I can't think of everything a user might want to use the framework for) - 
so letting users of the framework define their own runnable classes with 
the only criteria being that their class define a 'run' method made the 
whole system much simpler.  (BTW: I do check the 'contract' for an object 
prior to sending it out to a client - I make sure it responds_to 'run').

I know, it's difficult at first to move from the statically typed 
worldview to a dynamically typed worldview - it's kind of like looking at 
that popular optical illusion that looks at first like an old hag of a 
woman with a big nose, but as you stare at it a bit longer you 
see that within that image is a beautiful young woman.  It was like that 
for me initially as well, at first I missed having type checking, but now 
that I see it from the other side it is quite freeing and, dare I say it,  
beautiful.

Phil