against enforce

[Jonathan M Davis]

On 2011-03-26 08:55, Don wrote:
> spir wrote:
> > On 03/25/2011 11:20 PM, Jonathan M Davis wrote:
> >> In the case of something like dividing by 0 or other math functions
> >> that could
> >> be given bad values, the typical solution is to either use an
> >> assertion (or
> >> check nothing) and then let the caller worry about it. It would be
> >> extremely
> >> wasteful to have to constantly check whether the arguments to typical
> >> math
> >> functions are valid. They almost always are, and those types of
> >> functions needto be really efficient.
> > 
> > But catching wrong arguments to math functions at *runtime* is precisely
> > 
> > what D itself does (as well as all languages I know):
> >     auto a = 1, b = 0;
> >     auto c = a/b;
> > 
> > ==>
> > 
> >     Floating point exception
> > 
> > There is no way out, or do I miss a point?
> > 
> > Denis
> 
> That one is done by the CPU, as mentioned in another post. But it does
> illustrate something interesting: the contract programming makes you
> think there is a symmetry between in and out contracts, whereas in fact
> they have very little in common. If an out contract fails, it ALWAYS
> indicates a bug in the function. So it should ALWAYS be an assert.
> But 'in' contracts are completely different, since they indicate a
> problem in the calling code. (Personally I cannot see the value of 'out'
> contracts, except as information for verifying later 'in' contracts).

Whereas I _rarely_ use in contracts. In most cases, I favor exceptions, 
treating my functions as API functions pretty much as long as they're public. 
That's not always the best approach, but it's generally what I end up using.

invariants, I use fairly frequently (and in fact have run into trouble due to 
issues with them - e.g. http://d.puremagic.com/issues/show_bug.cgi?id=5058 ).

out, on the other hand, I don't use as much. It's not terribly common that 
there's a good test to run on the return value of a function in my experience. 
Upon occasion, it's useful, but rarely. Unit tests generally solve the problem 
better with regards to testing output. They're still useful though - just not 
commonly so.

So, honestly, other than invariants, I don't use D's DbC much. in contracts 
get used upon occasion, but I tend to favor exceptions over assertions in most 
cases, so I don't use in all that often, and while out is occasionally useful, 
unit tests generally do a better job of verifying that a function's return 
value is correct. I'm _very_ glad to have invariants though.

- Jonathan M Davis