Prefer transparent functors to non-transparent ones. When using transparent functors, the type does not need to be repeated. The code is easier to read, maintain and less prone to errors. It is not possible to introduce unwanted conversions.
// Non-transparent functor std::map<int, std::string, std::greater<int>> s; // Transparent functor. std::map<int, std::string, std::greater<>> s; // Non-transparent functor using MyFunctor = std::less<MyType>;
It is not always a safe transformation though. The following case will be untouched to preserve the semantics.
// Non-transparent functor std::map<const char *, std::string, std::greater<std::string>> s;