clang/test/CXX/over/over.match/over.match.viable/p3.cpp

   1 // RUN:  %clang_cc1 -std=c++2a -verify %s
   2
   3 struct S2 {};
   4 // expected-note@-1 {{candidate constructor (the implicit copy constructor) not viable: no known conversion from 'S1<int>' to 'const S2' for 1st argument}}
   5 // expected-note@-2 {{candidate constructor (the implicit move constructor) not viable: no known conversion from 'S1<int>' to 'S2' for 1st argument}}
   6 // expected-note@-3 {{candidate constructor (the implicit default constructor) not viable: requires 0 arguments, but 1 was provided}}
   7
   8 template<typename T>
   9 struct S1 {
  10   void foo() const requires true {}
  11   void foo() const requires false {}
  12   void bar() const requires false {}
  13   // expected-note@-1 {{because 'false' evaluated to false}}
  14   operator bool() const requires true { return true; }
  15   explicit operator bool() const requires false;
  16   explicit operator S2() const requires false;
  17   // expected-note@-1 {{candidate function not viable: constraints not satisfied}}
  18   // expected-note@-2 {{because 'false' evaluated to false}}
  19 };
  20
  21 void foo() {
  22   S1<int>().foo();
  23   S1<int>().bar();
  24   // expected-error@-1 {{invalid reference to function 'bar': constraints not satisfied}}
  25   (void) static_cast<bool>(S1<int>());
  26   (void) static_cast<S2>(S1<int>());
  27   // expected-error@-1 {{no matching conversion for static_cast from 'S1<int>' to 'S2'}}
  28 }
  29
  30 // Test that constraints are checked before implicit conversions are formed.
  31
  32 template<typename T>
  33 struct invalid_template { using X = typename T::non_existant; };
  34 struct A {
  35   template<typename T, bool=invalid_template<T>::aadasas>
  36   operator T() {}
  37 };
  38
  39 template<typename>
  40 struct WrapsStatics {
  41   static void foo(int) requires false;
  42   static void foo(A) requires true;
  43 };
  44
  45 template<typename T>
  46 struct S {
  47   void foo(int) requires false;
  48   void foo(A) requires true;
  49   S(A) requires false;
  50   S(double) requires true;
  51   ~S() requires false;
  52   ~S() requires true;
  53   operator int() requires true;
  54   operator int() requires false;
  55 };
  56
  57 void bar() {
  58   WrapsStatics<int>::foo(A{});
  59   S<int>{1.}.foo(A{});
  60
  61   S<int> s = 1;
  62   int a = s;
  63 }