https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86874
Bug ID: 86874
Summary: std::swap on std::variant fails to compile
Product: gcc
Version: 8.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: aaron at bestateless dot com
Target Milestone: ---
Created attachment 44514
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44514&action=edit
Preprocessed source.
Example:
#include <variant>
int main(int, char**) {
std::variant<std::monostate> v1, v2;
std::swap(v1, v2);
}
Expected: Compiles successfully. (Worked for me on g++ 7.3).
Actual:
```
$ g++-8 -v
Using built-in specs.
COLLECT_GCC=g++-8
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/8/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 8.2.0-1'
--with-bugurl=file:///usr/share/doc/gcc-8/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr
--with-gcc-major-version-only --program-suffix=-8
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie
--with-system-zlib --with-target-system-zlib --enable-objc-gc=auto
--enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 8.2.0 (Debian 8.2.0-1)
$ g++-8 -std=c++17 test.cpp -save-temps
In file included from test.cpp:1:
/usr/include/c++/8/variant: In instantiation of 'void
std::variant<_Types>::swap(std::variant<_Types>&) [with _Types =
{std::monostate}]':
/usr/include/c++/8/variant:1010:7: required from
'std::enable_if_t<((is_move_constructible_v<_Types> && ...) &&
(is_swappable_v<_Types> && ...))> std::swap(std::variant<_Types ...>&,
std::variant<_Types ...>&) [with _Types = {std::monostate};
std::enable_if_t<((is_move_constructible_v<_Types> && ...) &&
(is_swappable_v<_Types> && ...))> = void]'
test.cpp:5:21: required from here
/usr/include/c++/8/variant:1265:12: error: 'class std::variant<std::monostate>'
has no member named '_M_destructive_move'
this->_M_destructive_move(std::move(__rhs));
~~~~~~^~~~~~~~~~~~~~~~~~~
/usr/include/c++/8/variant:1270:12: error: 'class std::variant<std::monostate>'
has no member named '_M_destructive_move'
__rhs._M_destructive_move(std::move(*this));
~~~~~~^~~~~~~~~~~~~~~~~~~
/usr/include/c++/8/variant:1276:12: error: 'class std::variant<std::monostate>'
has no member named '_M_destructive_move'
__rhs._M_destructive_move(std::move(*this));
~~~~~~^~~~~~~~~~~~~~~~~~~
/usr/include/c++/8/variant:1277:12: error: 'class std::variant<std::monostate>'
has no member named '_M_destructive_move'
this->_M_destructive_move(std::move(__tmp));
~~~~~~^~~~~~~~~~~~~~~~~~~
```
