unique_storage.h

Go to the documentation of this file.

#ifndef UNIQUE_STORAGE_H
#define UNIQUE_STORAGE_H

#include <vector>
#include <map>
#include <stdexcept>

template <typename I, typename V> class unique_storage {

public:
    unique_storage() {
        // id 0
        values.push_back(V());
    }

    virtual ~unique_storage() {}

    typedef std::vector<V> stored_values;

    struct id_value {
        id_value() : id(0) {}

        bool set() const {
            return id;
        }

        bool operator<(id_value const & rhs) const {
            return id < rhs.id;
        }

        bool operator==(id_value const & rhs) const {
            return id == rhs.id;
        }

        bool operator!=(id_value const & rhs) const {
            return !(id == rhs.id);
        }

    private:
        friend class unique_storage<I, V>;

        typedef typename stored_values::size_type size_type;

        explicit id_value(size_type s) : id(s) {}

        size_type id;
    };


    id_value const create(V const & value) {
        typename id_map::value_type val(value, id_value(values.size()));
        std::pair<typename id_map::iterator, bool>
            inserted = ids.insert(val);
        if (inserted.second)
            values.push_back(value);

        return inserted.first->second;
    }


    V const & get(id_value const & id) const {
        // some stl lack at(), so we emulate it
        if (id.id < values.size())
            return values[id.id];

        throw std::out_of_range("unique_storage::get(): out of bounds");
    }

private:
    typedef std::map<V, id_value> id_map;

    stored_values values;

    id_map ids;
};

#endif /* !UNIQUE_STORAGE_H */