https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93698
Bug ID: 93698
Summary: ICE on concept using generic lambda
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Keywords: ice-on-valid-code
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: kretz at kde dot org
Target Milestone: ---
Test case (-std=c++2a):
template <int N> concept foo = [](auto) constexpr -> bool { return true;
}(N);
bool a = foo<2>;
Extended test case (use lambda in concept to turn integer into index sequence):
#include <utility>
template <int N>
concept foo = []<std::size_t... Is>(std::index_sequence<Is...>) constexpr {
return (Is + ...) > 10;
}(std::make_index_sequence<N>());
bool a = foo<7>;
If I read the standard correctly, both test cases are well-formed and should
work: P0315R4 started to allow lambdas in unevaluated contexts
(https://eel.is/c++draft/temp.concept#6).
On a slight tangent: I believe substitution failures on instantiation of the
lambda are not ill-formed, even though P0315R4 seemed to intend that outcome.
While I would love to use it to SFINAE test structured bindings, I think this
is rather a defect in the current WD, no?
