[swift-evolution] Support for assertions/preconditions that sometimes fail.

[Amir Michail]

> On Jan 14, 2017, at 8:00 PM, Saagar Jha <saagar at saagarjha.com> wrote:
> 
> Why not just add a // TODO or // FIXME comment?
> 

There is no bug. Moreover, you want something that actually executes and that can give you useful information when the program finishes running.

> Saagar Jha
> 
>> On Jan 14, 2017, at 4:10 PM, Amir Michail via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> It’s quite common for an assertion/precondition that you thought should hold actually does not yet there is no bug. In that case, you might want to remind yourself of this fact by commenting out the assertion/precondition (instead of deleting it) so that you don’t make the same mistake in the future by inserting such assertions/preconditions into the code.
>> 
>> However, it would be nice to have explicit support for assertions/preconditions that don’t always hold where there is no bug.
>> 
>> For example:
>> 
>> preconditionNotAlwaysTrue( list.isEmpty )
>> 
>> When your app finishes running, the IDE could show you all such preconditions/assertions that you thought fail sometimes that did not fail in that particular run. In that case, you might consider switching them to normal preconditions/assertions provided your code has now evolved to the point where they always hold.
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