From: gwtmp01@...
Date: 2006-04-02T22:58:34+09:00
Subject: Re: Typed Parameters


On Apr 2, 2006, at 9:29 AM, Austin Ziegler wrote:
> On 4/2/06, Robert Dober <robert.dober@gmail.com> wrote:
>> My programs often pass objects of an unexpected "contract, behavior,
>> type, mixin interface" you name it. I would like a modern language to
>> help me, the *stupid* programmer to be more *effective* Ruby claims
>> that.
>
> It's called "unit tests." If your programs are often passing objects
> that don't behave the way you want those objects to behave, then  
> it's a
> bug that you should be ensuring doesn't come out of the caller; in  
> Ruby
> it's often far more efficient to ensure that the caller doesn't  
> screw up
> instead of the callee doing checks ...

If I remember correctly from _Object Oriented Software Engineering_,
Betrand Meyer specifically talks about how when pre-conditions fail, it
is the *caller* that has violated the contract.  When a program is  
written
correctly (i.e., without bugs) pre-condition testing is completely  
superfluous
at run-time.  I think the Eiffel compilers even have a switch to turn- 
off
run-time pre-condition testing.

I'd rather see the support for pre-conditions and testing within the
context of the development environment rather than burdening the run- 
time
environment.  The use of annotations along with smart text editors and
test-case generators might be useful.

Gary Wright