https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99963
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jason at gcc dot gnu.org,
| |ppalka at gcc dot gnu.org
Target Milestone|--- |11.0
Summary|[concepts] template |[11 Regression] [concepts]
|<concept> vs concept auto |template <concept> vs
|reports ambiguous overload |concept auto reports
| |ambiguous overload
--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Started with r11-1571. Reduced testcase that replaces the abbreviated function
templates with their corresponding non-abbreviated forms:
template <class T> concept C1 = true;
template <class T> concept C2 = C1<T> && true;
template <C1 T, C1 U> int f(T, U);
template <C1 T, C2 U> int f(U, T);
int x = f(0, 0); // error: ambiguous call
If I understand the wording of P2113 correctly:
If deduction against the other template succeeds for both transformed
templates, constraints can be considered as follows:
- ... if the corresponding template-parameters of the
template-parameter-lists are not equivalent ([temp.over.link]) or if the
function parameters that positionally correspond between the two templates are
not of the same type, neither template is more specialized than the other
then I think we're correct to reject the call as ambiguous because although the
second overload is more constrained than the first, their function parameter
lists aren't equivalent.
