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 'not_bool::E'}}
29 }
30
31 struct X { bool equal; };
32 struct Y {};
operator ==(X x,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});
49