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

[Dmitri Gribenko]

On Tue, Mar 1, 2016 at 11:50 PM, Andrey Tarantsov via swift-evolution
<swift-evolution at swift.org> wrote:
> Whoa. Everyone seems to be in favor of this. Don't you guys always return
> something ‘just in case’, in the best traditions of C API design? I tend to
> have lots of discardable results and only a few where I might legitimately
> forget to use it.
>
> IMO, in most cases ignoring a return value is “safe”:
>
> a) If a method is called only for its result, forgetting to use the result
> won't really introduce any new bugs — if you're not using that missing
> result elsewhere, storing it into a variable won't help.
>
> b) If you're calling a method for its side effect, normally the result may
> be discarded.
>
> The only case where this matters is when the method establishes a long-term
> relationship (like a subscription) that needs to be stored to survive. That
> seems like a rare case.
>
> Any other practical cases?

The reason for warning on ignored "safe" returned values is that the
code calls the method, but it ignores the result.  Presumably, the
developer wrote the method call for a reason -- they wanted their code
to do something.  Nobody needs a fancy no-op in their code.  So while
discarding "safe" return values does not compromise memory safety or
introduce races or anything bad like that, there is a very high
probability that the code is just wrong and does not do what the
developer wanted.  It does something else, in a totally "safe" way.

Dmitri

-- 
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