Sometimes we need to use stl data structures such as map, unordered_map or set using a data type that doesn't have a hash or a comparator. Instead of coding things properly I will show an easy way to achieve the same thing with minimal effort.

Let's say we want to use pair<int,int> with a unordered_map. Notice that there's no pre-made hash for this data type.

The size of pair<int,int> is 8 bytes. Also notice that we have long long: a data type also 8 bytes long.

We can create an unordered_map, and to check our pair we can just do:

typedef std::pair<int,int> pii;
std::unordered_map<long long,int> hashmap;
pii object;
hashmap[*((long long*)&object)] = 24;

We can recast our data type for another data type of the same size, and it will work just fine! But we don't have endless ints to use. Is there an easier way that is able to store any data structure?

Luckly there is!

We can use bitsets, and resize them for the size we want. Following our previous example: cpp typedef std::pair<int,int> pii; typedef std::bitset<sizeof(pii)*8> bits; std::unordered_map<bits,int> hashmap; pii object; hashmap[*((bits*)&object)] = 24;

That's the way we can use unordered_map, sets or similar data structures without coding hashes or comparators!