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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
{
using value_type = int;
};
bool operator<(Combi const &lhs, Combi const &rhs);
Combi operator+(Combi const &lhs, Combi const &rhs);
template <typename Type>
struct Data
{
template <Constraint Member>
void process(Member par); // a member template is constrained
template <typename Tp> // also, now via a variable constr.
void another(Tp par) requires Constraint2<Tp>;
};
template <typename T1>
template <Constraint T2>
void Data<T1>::process(T2 par)
{}
template <typename T1>
template <typename T2>
void Data<T1>::another(T2 par) requires Constraint2<T2>
{}
int main()
{
Data<int>{}.process(Combi{});
}
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