From: Austin Ziegler <halostatue@...>
Date: 2006-02-08T23:56:19+09:00
Subject: Re: Meta-Meta-Programming

On 08/02/06, vidar.hokstad@gmail.com <vidar.hokstad@gmail.com> wrote:
> Daniel Nugent wrote:
>> Vidar, I think the question there is: Should I rely on a type/method
>> check to ensure that I don't get bad parameters or should I just
>> write some tests to make sure that the code in question fails in a
>> sensible way when those expectations aren't met. Those would be edge
>> cases after all, and you'd have to write the tests for them anyway.
>>
>> To me, it seems to be unDRY...
>
> To me the issue is to avoid surprises. If your function will need a
> specific method every few million times it is executed, or on specific
> dates, or when a specific race condition occurs, or when processing
> specific user input, it might require a lot of work for a user of your
> code to verify that their application works as expected through
> testing unless they know exactly what they need to test for.

That's what documentation is for.

> More importantly: Unless _they_ verify these preconditions in their
> test cases they will have to handle whatever you consider a "sensible
> way of failing". If your failure mode doesn't match their
> expectations, it might take a lot of work to set verify that there is
> actually a problem, and it can easily slip through.

That's what documentation is for.

> This is a pragmatic way of ensuring the least possibility of surprise,
> by forcing a failure as early as possible. The other alternative is to
> document these cases painstakingly and depend on the users of your
> code to test for them. But why put your users through that pain if you
> have an easy way of trapping the error early on that at the same time
> serves as explicit documentation of what your code expects?

Except that contract enforcement is *expensive*, and most contracts are
much more difficult to express than can be expressed in the way that
people who are (foolishly) comforted by static typing expect.

-austin
--
Austin Ziegler * halostatue@gmail.com
               * Alternate: austin@halostatue.ca