On 02/05/19 20:09 +0100, Jonathan Wakely wrote:
On 02/05/19 20:34 +0200, Stephan Bergmann wrote:
On 29/04/2019 15:26, Jonathan Wakely wrote:
* include/bits/move.h (swap(T&, T&), swap(T (&)[N], T (&)[N])): Use
_GLIBCXX_NOEXCEPT_IF to simplify declarations.
This just avoids having to repeat the name and parameter-list of the
functions.
libstdc++-v3/include/std/type_traits still has
template<typename _Tp>
inline
typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
is_move_constructible<_Tp>,
is_move_assignable<_Tp>>::value>::type
swap(_Tp&, _Tp&)
noexcept(__and_<is_nothrow_move_constructible<_Tp>,
is_nothrow_move_assignable<_Tp>>::value);
using noexcept instead of _GLIBCXX_NOEXPECT_IF, and at least during
configure of building LibreOffice with Clang, that causes failure
.../gcc/trunk/lib/gcc/x86_64-pc-linux-gnu/10.0.0/../../../../include/c++/10.0.0/bits/move.h:185:5:
error: exception specification in declaration does not match previous
declaration
swap(_Tp& __a, _Tp& __b)
^
.../gcc/trunk/lib/gcc/x86_64-pc-linux-gnu/10.0.0/../../../../include/c++/10.0.0/type_traits:2531:5:
note: previous declaration is here
swap(_Tp&, _Tp&)
^
I didn't try to track down under what conditions
_GLIBCXX_NOEXCEPT_IF would not expand to noexcept, but I assume that
just type_traits needs adapting, too?
That's weird. _GLIBCXX_NOEXCEPT_IF is only empty for C++11, in which
case the declaration in <type_traits> isn't seen anyway. And there's
no point using _GLIBCXX_NOEXCEPT_IF in <type_traits> because we can
(and should) just use noexcept directly in C++11 code. The macro
exists for code that needs to be compiled as C++98 too.
The only difference is that there's an extra set of parentheses around
the NOEXCEPT_IF condition, so the preprocessor doesn't try to eat the
comma.
So one declaration is:
template<typename _Tp>
inline
typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
is_move_constructible<_Tp>,
is_move_assignable<_Tp>>::value>::type
swap(_Tp&, _Tp&)
noexcept(__and_<is_nothrow_move_constructible<_Tp>,
is_nothrow_move_assignable<_Tp>>::value);
And the other is:
template<typename _Tp>
inline
typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
is_move_constructible<_Tp>,
is_move_assignable<_Tp>>::value>::type
swap(_Tp&, _Tp&)
noexcept((__and_<is_nothrow_move_constructible<_Tp>,
is_nothrow_move_assignable<_Tp>>::value));
Yep, Clang doesn't like that:
https://wandbox.org/permlink/clslE9PGCVtKPppz
Does adding the extra parens into type_traits fix it? i.e.
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -2529,8 +2529,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
is_move_constructible<_Tp>,
is_move_assignable<_Tp>>::value>::type
swap(_Tp&, _Tp&)
- noexcept(__and_<is_nothrow_move_constructible<_Tp>,
- is_nothrow_move_assignable<_Tp>>::value);
+ noexcept((__and_<is_nothrow_move_constructible<_Tp>,
+ is_nothrow_move_assignable<_Tp>>::value));
template<typename _Tp, size_t _Nm>
inline
