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template <typename Type>
concept bool Constraint() // function concept
{
return
requires(Type lhs, Type rhs)
{
{ lhs < rhs } -> bool; // multiple
lhs + rhs; // constraints
// typename Type::value_type;
};
}
template <typename Type>
concept bool Constraint2 = // variable concept
requires(Type lhs, Type rhs)
{
// { operator<(lhs, rhs) } -> bool; // both OK
{ lhs < rhs } -> bool;
lhs + rhs;
typename Type::value_type;
};
// template <typename Type> concept bool Constraint = true ;
struct Combi
{
typedef int value_type;
};
bool operator<(Combi const &lhs, Combi const &rhs);
Combi operator+(Combi const &lhs, Combi const &rhs);
template <Constraint Type> // declares a multiply
requires Constraint2<Type> void fun(); // constrained function template
int main()
{
fun<Combi>();
}
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