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template <typename Type>
concept bool Addable =
requires(Type lh, Type rh)
{
lh + rh;
};
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 <typename Type>
struct Data
{ // constraint applies only to a member
void process() requires Addable<Type>;
template <Addable Tp>
void add(Tp tp);
};
template <typename Typ> // formal type names may differ
void Data<Typ>::process() requires Addable<Typ> // from the class.
{}
template <typename Typ> // formal type names may differ
template <Addable Tp>
void Data<Typ>::add(Tp tp)
{}
int main()
{
Data<Combi>{}.process();
}
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