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

[Dmitri Gribenko]

On Wed, Mar 2, 2016 at 1:38 PM, David Owens II <david at owensd.io> wrote:
> Had the API been marked as discardable, there's no way to tell if you've
> made an oversight error or were being explicit about not needing the result.

The point you are making is true of any source-level annotations that
can't be verified by the compiler independently.  For example,
force-unwrapping an optional -- there is no way to tell, either for a
compiler or even another engineer, whether force-unwrapping is a logic
error or not.

Dmitri

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