[swift-evolution] Make non-void functions @warn_unused_result by default

[Riley Testut]

My initial gut reaction is that I don’t mind this change happening, but I would much prefer using a @suppress_unused_result attribute than forcing the user to "let _ = “. The API designer should know whether the return value is necessary or not, and make it easy for the consumer to decide whether they want to use it or not.

> On Dec 10, 2015, at 3:30 PM, Adrian Kashivskyy via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Matthew, I actually like your idea better than using an opposite "@suppress_unused_result" attribute. In addition, it will even be easier to implement, since "let _" syntax is already supported in the language.
> 
> Pozdrawiam – Regards,
> Adrian Kashivskyy
> 
>> Wiadomość napisana przez Matthew Johnson <matthew at anandabits.com <mailto:matthew at anandabits.com>> w dniu 11.12.2015, o godz. 00:28:
>> 
>> Why should unused results be acceptable?  Why not require callers to explicitly throw away the result:
>> 
>> let _ = funcReturningValueThatIsIgnored()
>> 
>> Yes this is extra syntax, but it also makes it clear that the value was intended to be ignored and the function was only executed for side-effects.  
>> 
>>> On Dec 10, 2015, at 5:23 PM, Guillaume Lessard via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>> 
>>>> On 10 déc. 2015, at 15:58, Adrian Kashivskyy via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>> 
>>>> I think non-void functions should warn about their return value being unused by default, thus eliminating the need to attribute them with @warn_unused_result.
>>> 
>>> I strongly don’t like this idea. This being said, if it happens ann attribute that says "unused result are acceptable" must be created. Makes me wince.
>>> 
>>> Guillaume Lessard
>>> 
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