1 // RUN: %clang_cc1 -fsyntax-only -verify -std=c++2a %s 2 3 template <typename T1, typename T2> struct is_same { 4 static constexpr bool value = false; 5 }; 6 7 template <typename T> struct is_same<T, T> { 8 static constexpr bool value = true; 9 }; 10 11 template <class T, class U> 12 concept SameHelper = is_same<T, U>::value; 13 template <class T, class U> 14 concept same_as = SameHelper<T, U> && SameHelper<U, T>; 15 16 namespace deferred_instantiation { do_not_instantiate()17template <class X> constexpr X do_not_instantiate() { return nullptr; } 18 19 struct T { Tdeferred_instantiation::T20 template <same_as<float> X> explicit(do_not_instantiate<X>()) T(X) {} 21 Tdeferred_instantiation::T22 T(int) {} 23 }; 24 25 T t(5); 26 // expected-error@17{{cannot initialize}} 27 // expected-note@20{{in instantiation of function template specialization}} 28 // expected-note@30{{while substituting deduced template arguments}} 29 // expected-note@30{{in instantiation of function template specialization}} 30 T t2(5.0f); 31 } // namespace deferred_instantiation 32