namespace std {
template <class T = void>
struct default_order {
using type = less<T>;
};
}
The class template default_order provides a trait that users can specialize for user-defined types to provide a strict weak ordering for that type, which the library can use where a default strict weak order is needed. For example, the associative containers ([associative]) and priority_queue ([priority.queue]) use this trait.
[ Example:
namespace sales {
struct account {
int id;
std::string name;
};
struct order_accounts {
bool operator()(const Account& lhs, const Account& rhs) const {
return lhs.id < rhs.id;
}
};
}
namespace std {
template<>
struct default_order<sales::account> {
using type = sales::order_accounts;
};
}
— end example ]