This is a regression caused by merging #2687 in VS 2022 17.3 Preview 2:
#include <utility>
using namespace std;
struct __declspec(dllexport) MyPair : pair<int, int> {};C:\Temp>cl /EHsc /nologo /W4 /MD /c /std:c++20 meow.cpp
meow.cpp
C:\Temp>cl /EHsc /nologo /W4 /MD /c /std:c++latest meow.cpp
meow.cpp
C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.33.31629\include\utility(107): error C2672: 'swap': no matching overloaded function found
C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.33.31629\include\type_traits(1965): note: could be 'void std::swap(_Ty (&)[_Size],_Ty (&)[_Size]) noexcept(<expr>)'
C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.33.31629\include\utility(107): note: 'void std::swap(_Ty (&)[_Size],_Ty (&)[_Size]) noexcept(<expr>)': could not deduce template argument for '_Ty (&)[_Size]' from '_Ty'
with
[
_Ty=int
]
C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.33.31629\include\type_traits(1965): note: see declaration of 'std::swap'
C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.33.31629\include\type_traits(1962): note: or 'void std::swap(_Ty &,_Ty &) noexcept(<expr>)'
C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.33.31629\include\utility(106): note: 'void std::swap(_Ty &,_Ty &) noexcept(<expr>)': could not deduce template argument for '_Enabled'
C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.33.31629\include\type_traits(1962): note: see declaration of 'std::swap'
C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.33.31629\include\utility(408): note: see reference to function template instantiation 'void std::_Swap_adl<const _Ty1>(_Ty &,_Ty &) noexcept(false)' being compiled
with
[
_Ty1=int,
_Ty=int
]
C:\Program Files\Microsoft Visual Studio\2022\Preview\VC\Tools\MSVC\14.33.31629\include\utility(406): note: while compiling class template member function 'void std::pair<int,int>::swap(const std::pair<int,int> &) noexcept(false) const'
meow.cpp(4): note: see reference to class template instantiation 'std::pair<int,int>' being compiled
Relevant code:
|
#if _HAS_CXX23
|
|
constexpr void swap(const pair& _Right) const
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noexcept(is_nothrow_swappable_v<const _Ty1>&& is_nothrow_swappable_v<const _Ty2>) {
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if (this != _STD addressof(_Right)) {
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_Swap_adl(first, _Right.first);
|
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_Swap_adl(second, _Right.second);
|
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}
|
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}
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#endif // _HAS_CXX23
|
WG21-N4910 [pairs.pair]/45.2 says:
Mandates: For the second overload, is_swappable_v<const T1> is true and is_swappable_v<const T2> is true.
So we aren't supposed to constrain this, but that interacts badly with dllexport which tries to instantiate everything.
I suspect that we need the template <int = 0> workaround, also applied to tuple.
Originally reported as DevCom-10109884 and internal VSO-1586226 / AB#1586226 .
This is a regression caused by merging #2687 in VS 2022 17.3 Preview 2:
Relevant code:
STL/stl/inc/utility
Lines 331 to 339 in 2263d93
WG21-N4910 [pairs.pair]/45.2 says:
So we aren't supposed to constrain this, but that interacts badly with
dllexportwhich tries to instantiate everything.I suspect that we need the
template <int = 0>workaround, also applied totuple.Originally reported as DevCom-10109884 and internal VSO-1586226 / AB#1586226 .