clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p9-2a.cpp

   1 // RUN: %clang_cc1 -std=c++2a -verify %s
   2
   3 // ... return type shall be cv bool ...
   4 namespace not_bool {
   5   struct X {} x;
   6   struct Y {} y;
   7   double operator==(X, Y); // expected-note 4{{here}}
   8   bool a = x == y; // ok
   9   bool b = y == x; // expected-error {{return type 'double' of selected 'operator==' function for rewritten '==' comparison is not 'bool'}}
  10   bool c = x != y; // expected-error {{return type 'double' of selected 'operator==' function for rewritten '!=' comparison is not 'bool'}}
  11   bool d = y != x; // expected-error {{return type 'double' of selected 'operator==' function for rewritten '!=' comparison is not 'bool'}}
  12
  13   // cv-qualifiers are OK
  14   const bool operator==(Y, X);
  15   bool e = y != x; // ok
  16
  17   // We don't prefer a function with bool return type over one witn non-bool return type.
  18   bool f = x != y; // expected-error {{return type 'double' of selected 'operator==' function for rewritten '!=' comparison is not 'bool'}}
  19
  20   // As an extension, we permit integral and unscoped enumeration types too.
  21   // These are used by popular C++ libraries such as ICU.
  22   struct Z {} z;
  23   int operator==(X, Z); // expected-note {{here}}
  24   bool g = z == x; // expected-warning {{ISO C++20 requires return type of selected 'operator==' function for rewritten '==' comparison to be 'bool', not 'int'}}
  25
  26   enum E {};
  27   E operator==(Y, Z); // expected-note {{here}}
  28   bool h = z == y; // expected-warning {{ISO C++20 requires return type of selected 'operator==' function for rewritten '==' comparison to be 'bool', not 'E'}}
  29 }
  30
  31 struct X { bool equal; };
  32 struct Y {};
  33 constexpr bool operator==(X x, Y) { return x.equal; }
  34
  35 static_assert(X{true} == Y{});
  36 static_assert(X{false} == Y{}); // expected-error {{failed}}
  37
  38 // x == y -> y == x
  39 static_assert(Y{} == X{true});
  40 static_assert(Y{} == X{false}); // expected-error {{failed}}
  41
  42 // x != y -> !(x == y)
  43 static_assert(X{true} != Y{}); // expected-error {{failed}}
  44 static_assert(X{false} != Y{});
  45
  46 // x != y -> !(y == x)
  47 static_assert(Y{} != X{true}); // expected-error {{failed}}
  48 static_assert(Y{} != X{false});