Hi, I'm trying to move away from Qt containers in my source code, and Qt 5.15 makes that a bit easier by providing specialisations for some its types. Now I have a struct S { QLatin1String a, b; } that I'd like to hash. I can use boost::hash_combine to implement std::hash<S>, but S is actually a nested type, and with qHash(), I could just write an overload as a hidden friend, and I figured I could do the same with hash_value() (at the cost of having to specify boost::hash<S> as a unordered_map template argument). But hash_combine seems to insist on hash_value which in turn doesn't look at std::hash at all: size_t seed = 0; boost::hash_combine(seed, key.a); // ERROR: no hash_value overload for QLatin1String boost::hash_combine(seed, key.b); // Ditto return seed; expected: calls std::hash<QLatin1String>{}::op() (if it exists). It's trivial to write hash_value(QLatin1String), of course, but what's the general strategy here? Shouldn't hash_combine() look for std::hash<T> first? And, speaking as a Qt developer: do I really need to provide qHash(), std::hash<T> _and_ hash_value(T) for every hashable T?! Thanks, Marc