Detect default implementation of THashHelper

4ef7a7a8f6c8008dc1203097922562c21bf12bfb

Author: yurial

util/str_stl.h

@@ -37,6 +37,8 @@ namespace std {
 namespace NHashPrivate {
     template <class T, bool needNumericHashing>
     struct THashHelper {
+        using is_default_implementation = std::true_type;
+
         inline size_t operator()(const T& t) const noexcept {
             return (size_t)t; // If you have a compilation error here, look at explanation below:
             // Probably error is caused by undefined template specialization of THash<T>