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<tuple>: LWG-3528 make_from_tuple can perform (the equivalent of) a C-style cast #2160

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Merged
StephanTLavavej merged 2 commits into from
Sep 2, 2021
Merged

<tuple>: LWG-3528 make_from_tuple can perform (the equivalent of) a C-style cast #2160

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cbdca06
Adopt LWG-3528
frederick-vs-ja Aug 26, 2021
733b44a
Adopt CaseyCarter's suggestions
frederick-vs-ja Aug 26, 2021
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6 changes: 4 additions & 2 deletions stl/inc/tuple
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Original file line number Diff line number Diff line change
Expand Up @@ -981,8 +981,10 @@ constexpr decltype(auto) apply(_Callable&& _Obj, _Tuple&& _Tpl) { // invoke _Obj
}

template <class _Ty, class _Tuple, size_t... _Indices>
constexpr _Ty _Make_from_tuple_impl(
_Tuple&& _Tpl, index_sequence<_Indices...>) { // construct _Ty from the elements of _Tpl
constexpr _Ty _Make_from_tuple_impl(_Tuple&& _Tpl, index_sequence<_Indices...>) {
// construct _Ty from the elements of _Tpl
static_assert(is_constructible_v<_Ty, decltype(_STD get<_Indices>(_STD forward<_Tuple>(_Tpl)))...>,
"the target type must be constructible from the fields of the argument tuple (N4892 [tuple.apply]/2).");
return _Ty(_STD get<_Indices>(_STD forward<_Tuple>(_Tpl))...);
}

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