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Wrong constraint for std::optional<T>::operator=(U&&) #37986

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jwakely mannequin opened this issue Aug 20, 2018 · 2 comments
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Wrong constraint for std::optional<T>::operator=(U&&) #37986

jwakely mannequin opened this issue Aug 20, 2018 · 2 comments
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bugzilla compile-fail libc++

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@jwakely
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Mannequin

@jwakely jwakely mannequin commented Aug 20, 2018

Bugzilla Link 38638
Resolution FIXED
Resolved on Jun 27, 2019 11:41
Version 6.0
OS All
CC @dwblaikie,@mclow

Extended Description

The following should compile:

#include
constexpr int foo(int i) {
std::optional o;
o = i;
return *o;
}

Wandbox tells me:

prog.cc:2:15: error: constexpr function never produces a constant expression [-Winvalid-constexpr]
constexpr int foo(int i) {
^
prog.cc:4:5: note: non-constexpr function 'operator=<int &, void>' cannot be used in a constant expression
o = i;
^
/opt/wandbox/clang-6.0.0/include/c++/v1/optional:773:5: note: declared here
operator=(_Up&& __v)
^

https://wandbox.org/permlink/OrXOqTuQHDSddHod

The note shows that operator=(U&&) is being used, but that should not participate in overload resolution unless conjunction_v<is_scalar, is_same<T, decay_t>> is false.

In my code is_scalar is true, and is_same<int, decay_t<int&>> is true.

@jwakely
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@jwakely jwakely mannequin commented Aug 20, 2018

In my code is_scalar is true, and is_same<int, decay_t<int&>> is true.

Actually, in all code is_scalar is true, I'm not special ;-)

@mclow
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@mclow mclow commented Jun 27, 2019

Fixed in revision 364574.

@llvmbot llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 10, 2021
This issue was closed.
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