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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>
struct Data
{
void process();
};
// template <Constraint X> // Constraint may or may not be specified
template <typename X> // as the constraints are implied by Data
void Data<X>::process() // the formal typename may also be different
{}
template <Constraint2 Type>
struct Data2
{
void process();
};
template <Constraint2 X> // Constraint must be specified,
void Data2<X>::process() // but the formal type name
{ // doesn't have to be Type
int x = 0;
int y = x;
x = y << 1;
}
template <Constraint2 Type>
struct Data3
{
void process();
};
template <Constraint2 X> // Constraint must be specified,
void Data3<X>::process() // but the formal type name
{ // doesn't have to be Type
int x = 0;
int y = x;
x = y << 1;
}
int main()
{
Data<Combi>{}.process();
Data2<Combi>{}.process();
}
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