unordered-set

I'm using a std::unordered_set for the first time and have a question about the hash function. As far as I understand, if you don't specify a hash function it will default to std::hash<Key> . I have a mySet member in one of my classes: typedef std::unordered_set<MyClass> USetType; USetType mySet; When I try to build, I get the following error: error C2440: 'type cast' : cannot convert from 'const MyClass' to 'size_t' Is it necessary to define a conversion function (to size_t ) if you want to use unordered_set with a custom class? Is there any way to avoid writing your own hash function and

I have the following code to make an unordered_set<Interval> . This compiles fine. struct Interval { unsigned int begin; unsigned int end; bool updated; //true if concat. initially false int patternIndex; //pattern index. valid for single pattern int proteinIndex; //protein index. for retrieving the pattern }; struct Hash { size_t operator()(const Interval &interval); }; size_t Hash::operator()(const Interval &interval){ string temp = to_string(interval.begin) + to_string(interval.end) + to_string(interval.proteinIndex); return hash<string>()(temp); } unordered_set<Interval, string, Hash> test

Why doesn't std::unordered_map<tuple<int, int>, string> just work out of the box? It is tedious to have to define a hash function for tuple<int, int> , e.g. template<> struct do_hash<tuple<int, int>> { size_t operator()(std::tuple<int, int> const& tt) const {...} }; Building an unordered map with tuples as keys (Matthieu M.) shows how to automate this for boost::tuple . Is there anyway of doing this for c++0x tuples without using variadic templates? Surely this should be in the standard :( This works on gcc 4.5 allowing all c++0x tuples containing standard hashable types to be members of

To support user-defined key types in std::unordered_set<Key> and std::unordered_map<Key, Value> one has to provide operator==(Key, Key) and a hash functor: struct X { int id; /* ... */ }; bool operator==(X a, X b) { return a.id == b.id; } struct MyHash { size_t operator()(const X& x) const { return std::hash<int>()(x.id); } }; std::unordered_set<X, MyHash> s; It would be more convenient to write just std::unordered_set<X> with a default hash for type X , like for types coming along with the compiler and library. After consulting C++ Standard Draft N3242 §20.8.12 [unord.hash] and §17.6.3.4