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// { dg-do compile { target c++17_only } }
// { dg-options "-fconcepts" }
// Test that constraint satisfaction checks work even when
// processing template declarations.
namespace std
{
struct ostream { };
ostream cout;
template<typename T>
auto begin(T& t) -> decltype(t.begin()) { return t.begin(); }
template<typename T>
auto begin(T const& t) -> decltype(t.begin()) { return t.begin(); }
template<typename T>
auto end(T& t) -> decltype(t.end()) { return t.end(); }
template<typename T>
auto end(T const& t) -> decltype(t.end()) { return t.end(); }
} // namespace std
template <typename T>
concept bool Float()
{
return __is_same_as( T, float );
}
template <typename T>
constexpr decltype(auto) project( T t )
{
return t;
}
template <typename T>
concept bool Concept()
{
return requires( T t ) { // { dg-message "in requirements" }
requires Float<decltype( project(t) )>();
};
}
template <Concept E, Concept F>
constexpr decltype(auto) operator<<( E&& e, F&& f ) {}
template <Concept T>
void foo( T t )
{
// Try to resolve operator<< from within a template context but
// with non-dependent arguments. We need to ensure that template
// processing is turned off whenever checking for satisfaction.
std::cout << "OK"; // { dg-error "no match" }
}
template <typename R>
concept bool Range()
{
return requires( R r ) {
requires __is_same_as(
decltype(std::begin(r)), decltype(std::end(r)) );
};
}
struct A
{
A() = default;
A( const A& ) = default;
// Derivation from this class forces the instantiation of
// this constructor, which results in the __is_same_as type
// trait above to become error_mark_node in this declaration.
template <Range R>
explicit A( R&& r ) { }
};
struct C : A
{
C() = default;
C( const C& ) = default;
};
int main()
{
C c; // OK
return 0;
}
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