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Section: 184.108.40.206 [func.wrap.func] Status: C++17 Submitter: Agustín Bergé Opened: 2014-07-12 Last modified: 2017-07-30
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function<void(ArgTypes...)> should discard the return value of the target object. This behavior was in the original proposal, and it was removed (accidentally?) by the resolution of LWG 870.
Previous resolution [SUPERSEDED]:
Edit 220.127.116.11 [func.wrap.func] paragraph 2:
A callable object f of type F is Callable for argument types ArgTypes and return type R if the expression INVOKE(f, declval<ArgTypes>()...
, R), considered as an unevaluated operand (Clause 5), is well formed (22.10.4 [func.require]).
[2014-10-05 Daniel comments]
This side-effect was indeed not intended by 870.
STL provides improved wording. It replaces the current PR, and intentionally leaves 18.104.22.168 [func.wrap.func] unchanged.Due to 7 [expr]/6, static_cast<void> is correct even when R is const void.
This wording is relative to N4431.
Edit 22.10.4 [func.require] as depicted:
-2- Define INVOKE(f, t1, t2, ..., tN, R) as INVOKE(f, t1, t2, ..., tN) implicitly converted to R.
Change 22.214.171.124.5 [func.wrap.func.inv] as depicted:
R operator()(ArgTypes... args) const;
Effects: INVOKE(f, std::forward<ArgTypes>(args)..., R) (20.9.2), where f is the target object (20.9.1) of *this. -2- Returns: Nothing if R is void, otherwise the return value of INVOKE(f, std::forward<ArgTypes>(args)..., R).