/**
 * Retrieves an element from the given associative container.
 *
 * This is a std::map::at() replacement for environments that do not provide it.
 * It fails an @a assert() check or throws an exception if the requested element
 * does not exist.
 */
template<typename MapT>
typename MapT::mapped_type const& const_at(typename MapT::key_type const& key, MapT const& map)
{
    typename MapT::const_iterator it = map.find(key);
    if(it == map.end()) {
        assert(it != map.end());
        throw std::out_of_range("item_at()"); // Shouldn't get here without disabling assert()
    }
    return it->second;
}