[swift-users] Parameter Validation

[Dmitri Gribenko]

precondition() is enabled for release builds.

On Mon, Dec 7, 2015 at 5:24 PM, David Hart via swift-users <
swift-users at swift.org> wrote:

> You enable assertions for release builds then? Remember, I'm talking
> specifically about library code: the same way that calling NSArray's
> objectAtIndex throws an exception (if my memory serves well) for out of
> bounds indices. At least, NSAssert in Objective-C throws exceptions and is
> catchable.
>
> On 08 Dec 2015, at 01:43, Jens Alfke via swift-users <
> swift-users at swift.org> wrote:
>
>
> On Dec 7, 2015, at 11:39 AM, Jan Neumüller via swift-users <
> swift-users at swift.org> wrote:
>
> I fail to see any overhead here. Its the absolute minimum to get checked
> values. Anything less is not checking.
>
>
> There’s no overhead if the function already ‘throws’ / returns errors. But
> not all functions do that (and some functions _cannot_ do that, like
> operators.) If a function has to be upgraded to return an error, that _is_
> extra overhead, mostly on the caller’s side. (And, as previously noted,
> this may complicate the programmer’s life too, because now they may have to
> either propagate ‘throws’ to the caller or add a ‘catch’ handler.)
>
> Anyway, the programming conventions have been clear for a very long time:
> assertions should be used for programmer errors (like invalid parameters)
> while returned errors should be used for legitimate runtime error
> situations (like file-not-found). This predates Swift and even predates Mac
> OS X*; I think it goes back to OpenStep in the mid-‘90s.
>
> —Jens
>
> * NSError itself isn’t that old, but before that the APIs still returned
> nil or false for runtime errors.
>
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-- 
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/
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