C++ - Optimal way to use multiple values as a key in unordered_map

Question

I'm programming the class for working with state-spaces. My problem is, that I don't know, what's the ideal way to use multiple values as a key in unordered_map.

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It's supposed to work this way:

I create the state object with values <1;0;8>, so it'll be inserted into the hashmap as <1;0;8>:pointer_to_object. I want the hashmap because I need to find objects as fast as possible.

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I thought about using vector or tuple.

Is it possible to use one of them as a key for unordered_map without specifying their size in advance?

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EDIT:

I've tried to use the code recommended by @the_mandrill like this:

template <class T>
typedef std::unordered_map<std::vector<T>, State<T>*, boost::hash<std::vector<T>> Map;

template <class T>
size_t hash_value(const std::vector<T>& vec)
{
    std::size_t seed = 0;
    for (const auto& val : vec) {
      boost::hash_combine(seed, val);
    }
    return seed;
}

But I'm getting this error:

stateSpaceLib.cpp:79:83: error: template argument 3 is invalid
 typedef std::unordered_map<std::vector<T>, State<T>*, boost::hash<std::vector<T>> Map;
                                                                                   ^
stateSpaceLib.cpp:79:1: error: template declaration of ‘typedef’
 typedef std::unordered_map<std::vector<T>, State<T>*, boost::hash<std::vector<T>> Map;
 ^

Answer 1

You should be able to use a vector - either on its own or wrap it in a struct with any other state data you need, and then if you have access to boost then use hash_combine:

typedef std::unordered_map<std::vector<int>, ObjectPointer, boost::hash<std::vector<int>> Map;

size_t hash_value(const std::vector<int>& vec)
{
    std::size_t seed = 0;
    for (const auto& val : vec) {
      boost::hash_combine(seed, val);
    }
    return seed;
 }