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template <typename Type>
concept Comparable = // function concept
requires(Type lhs, Type rhs)
{
// { operator<(lhs, rhs) } -> bool; // multiple
lhs + rhs; // constraints
typename Type::value_type;
};
template <typename Type>
concept Comparable2 = // variable concept
requires(Type lhs, Type rhs)
{
// { operator<(lhs, rhs) } -> bool;
lhs + rhs;
typename Type::value_type;
};
template<Comparable Type> // concept names can be function
Type const &min1(Type const &x, Type const &y) // and variable concepts
{
return y < x ? y : x;
}
template<Comparable2 Type>
Type const &min2(Type const &x, Type const &y)
{
return y < x ? y : x;
}
template<typename Type> requires Comparable2<Type> // cannot be fun. con.
Type const &min3(Type const &x, Type const &y)
{
return y < x ? y : x;
}
struct Combi
{
typedef int value_type;
};
bool operator<(Combi const &lhs, Combi const &rhs);
Combi operator+(Combi const &lhs, Combi const &rhs);
int main()
{
min1(Combi{}, Combi());
min2(Combi{}, Combi());
min3(Combi{}, Combi());
}
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