[Bug c++/36587] Feature: add warning for constructor call with discarded return.

["kkylheku at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #4 from kkylheku at gmail dot com  2009-12-11 02:34 -------
(In reply to comment #3)
> This would have prevented bugs I've dealt with where critical sections where
> not protected:
> {
>   lock_guard (mutex);
>   // mutex NOT locked here!
> }
> But I'm not convinced that doing this is always a mistake.

Since we don't care about the object, we must care about the constructor side
effect. I seem to be under the impression that ISO C++ allows the construction
of temporary objects to be optimized away---even if there are side effects in
the constructor or destructor! Therefore, it's hard to see a valid use case for
this.

 Would the warning be
> suppressed by casting to void?
>   (void) TypeWithSideEffectsInCtor(x);

Not as implemented, I am afraid. The diagnostic is still produced that the
object is discarded. This is can be regarded as a flaw; something explicitly
requested by a cast should not be diagnosed.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36587