https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96803
Bug ID: 96803
Summary: std::tuple chooses wrong constructor for
uses-allocator construction
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Keywords: rejects-valid
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
#include <tuple>
#include <memory>
struct X
{
using allocator_type = std::allocator<int>;
X(X&&) { }
X(std::allocator_arg_t, const allocator_type&, X&&) { }
explicit X(int) { }
explicit X(int, allocator_type) { }
};
int main()
{
std::tuple<int> o(0);
std::tuple<X> ok(o);
std::tuple<X> nok(std::allocator_arg, std::allocator<int>(), o);
}
The last line of main fails:
In file included from tup.C:1:
/home/jwakely/gcc/10/include/c++/10.2.1/tuple: In instantiation of
'std::_Head_base<_Idx, _Head, true>::_Head_base(std::__uses_alloc1<_Alloc>,
_UHead&&) [with _Alloc = std::allocator<int>; _UHead = const int&; long
unsigned int _Idx = 0; _Head = X]':
/home/jwakely/gcc/10/include/c++/10.2.1/tuple:421:43: required from
'std::_Tuple_impl<_Idx, _Head>::_Tuple_impl(std::allocator_arg_t, const
_Alloc&, const std::_Tuple_impl<_Idx, _UHead>&) [with _Alloc =
std::allocator<int>; _UHead = int; long unsigned int _Idx = 0; _Head = X]'
/home/jwakely/gcc/10/include/c++/10.2.1/tuple:775:70: required from
'std::tuple<_Elements>::tuple(std::allocator_arg_t, const _Alloc&, const
std::tuple<_Args2 ...>&) [with _Alloc = std::allocator<int>; _UElements =
{int}; bool _Valid = true; typename
std::enable_if<std::tuple<_Elements>::_TCC<_Valid>::__is_explicitly_constructible<const
_UElements& ...>(), bool>::type <anonymous> = false; _Elements = {X}]'
tup.C:19:65: required from here
/home/jwakely/gcc/10/include/c++/10.2.1/tuple:110:65: error: no matching
function for call to 'X::X(const std::allocator_arg_t&, const
std::allocator<int>&, const int&)'
110 | : _Head(allocator_arg, *__a._M_a, std::forward<_UHead>(__uhead)) { }
| ^
tup.C:12:12: note: candidate: 'X::X(int, X::allocator_type)'
12 | explicit X(int, allocator_type) { }
| ^
tup.C:12:12: note: candidate expects 2 arguments, 3 provided
tup.C:11:12: note: candidate: 'X::X(int)'
11 | explicit X(int) { }
| ^
tup.C:11:12: note: candidate expects 1 argument, 3 provided
tup.C:9:3: note: candidate: 'X::X(std::allocator_arg_t, const allocator_type&,
X&&)'
9 | X(std::allocator_arg_t, const allocator_type&, X&&) { }
| ^
tup.C:9:50: note: no known conversion for argument 3 from 'const int' to
'X&&'
9 | X(std::allocator_arg_t, const allocator_type&, X&&) { }
| ^~~
tup.C:8:3: note: candidate: 'X::X(X&&)'
8 | X(X&&) { }
| ^
tup.C:8:3: note: candidate expects 1 argument, 3 provided
The problem is that the __use_alloc call in _Tuple_impl uses the wrong type.
