https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67150
Bug ID: 67150
Summary: [c++-concepts] Expression constraint fails with
dependent types
Product: gcc
Version: c++-concepts
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: Casey at Carter dot net
Target Milestone: ---
r226725 fails to compile this program:
#include <type_traits>
template <class From, class To>
concept bool ExplicitlyConvertible =
requires (From&& val) {
requires std::is_same<From,bool>::value;
requires std::is_same<To,bool>::value;
requires std::is_same<decltype(val),bool&&>::value;
static_cast<bool>((bool&&)val); // Line 9
static_cast<To>((From&&)val); // Line 10
};
template <class T>
concept bool Boolean =
requires (const T& t) {
{ t } -> ExplicitlyConvertible<bool>;
};
constexpr bool f(Boolean) { return true; } // Line 19
static_assert(f(true)); // Line 20
with error:
~/concept-gcc-r226725/bin/g++ -std=gnu++1z foo.cpp -c
foo.cpp:20:21: error: cannot call function ‘constexpr bool f(auto:1) [with
auto:1 = bool]’
static_assert(f(true)); // Line 20
^
foo.cpp:19:16: note: constraints not satisfied
constexpr bool f(Boolean) { return true; } // Line 19
^
foo.cpp:19:16: note: concept ‘Boolean<bool>’ was not satisfied
It does compile correctly if line 10 is commented out, demonstrating that the
expression "static_cast<To>((From&&)val)" is causing the constraint
dissatisfaction despite the fact that From is bool, To is bool, and
"static_cast<bool>((bool&&)val)" is acceptable.
