Viewing file:  concepts-class.C (2.49 KB) -rw-r--r--
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// { dg-do compile { target c++20 } }
template<typename T>
concept Class = __is_class(T);
template<typename T>
concept Union = __is_union(T);
template<typename T>
concept One = sizeof(T) >= 4;
template<typename T>
concept Two = One<T> && sizeof(T) >= 8;
// Basic checks
template<typename T> requires true struct ok { };
template<typename T> requires false struct err { };
ok<int> ok1;
err<int> err1; // { dg-error "template constraint failure" }
err<int>* err2; // { dg-error "template constraint failure" }
// Redeclarations
template<typename T>
requires Class<T>
struct S1;
template<Class T> // { dg-error "template parameter | different constraints" }
struct S1 { };
template<typename T>
requires Class<T>
struct S2;
template<typename T>
requires Union<T>
struct S2; // { dg-error "redeclaration | different constraints" }
// Check non-overlapping specializations
template<typename T>
struct S3 { static const int value = 0; };
template<typename T>
requires Class<T>
struct S3<T> { static const int value = 1; };
template<typename T>
requires Union<T>
struct S3<T> { static const int value = 2; };
struct S { };
union U { };
static_assert(S3<int>::value == 0, "");
static_assert(S3<S>::value == 1, "");
static_assert(S3<U>::value == 2, "");
// Check ordering of partial specializations
template<typename T>
struct S4 { static const int value = 0; };
template<typename T>
requires One<T>
struct S4<T> { static const int value = 1; };
template<typename T>
requires Two<T>
struct S4<T> { static const int value = 2; };
struct one_type { char x[4]; };
struct two_type { char x[8]; };
static_assert(S4<char>::value == 0, "");
static_assert(S4<one_type>::value == 1, "");
static_assert(S4<two_type>::value == 2, "");
// Specializations are more specialized.
template<typename T> requires Two<T> struct S5 { };
template<typename T> requires One<T> struct S5<T> { }; // { dg-error "does not specialize" }
// Constraints are checked even when decls are not instantiatied.
S5<one_type>* x4b; // { dg-error "constraint|invalid" }
// Deduction guides
template <class T>
concept IsInt = __is_same_as(T,int);
template<typename T>
struct A
{
int i;
A(...);
};
template<typename I>
requires IsInt<I>
A(I) -> A<I>;
A a(1);
A a2(1.0); // { dg-error "class template argument deduction | no matching function for call" }
template<typename T>
struct S6
{
template<typename U>
requires true
struct Inner;
};
template<typename T>
template<typename U>
struct S6<T>::Inner { }; // { dg-error "does not match" }
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