C++ map with 2 keys, such that any 1 key can be used to get the value

Question

I have a use case wherein I have to get a value from a map, given a key. Now the key can be ID (integer) or Name (string).

I thought about the following structure

map1:- ID -> value

map2:- Name -> ID

And hide this structure under a common abstraction, so that either name or ID can be used to retrieve the value.

Is there a better way to do this?

Answer 1

Have a look at boost::multi_index . It allows you to make containers with any combination of lookup that you want.

struct item
{
    int ID;
    std::string Name;
    value_t Value;
};

namespace bmi = boost::multi_index;
using map_t = bmi::multi_index_container<item, bmi::indexed_by<
    bmi::unordered_unique<bmi::tag<struct ID>, bmi::member<item, int, &item::ID>>,
    bmi::unordered_unique<bmi::tag<struct Name>, bmi::member<item, std::string, &item::Name>>
>>;

map_t Map;
/* add some values */
auto idIt = Map.get<ID>().find(1); // lookup by ID
auto nameIt = Map.get<Name>().find("Vaibhav Gupta"); // lookup by Name