**Are you tired of creating comparators or hashes for your custom class? I have a solution for you.**↵
↵
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.↵
↵
The idea is to use pointer casting.↵
↵
Let's say we want to use pair<int,int> with an 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<long long>, 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 integers to use. Is there an easier way that is able to store any data structure?↵
↵
Luckily there is!↵
↵
We can use bitsets, and resize them as we wish.↵
Following our previous example:↵
↵
```↵
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;↵
```↵
↵
Here we create a bitset exactly the size of our class, making us able to use any standard container with our pair<int,int>.↵
↵
Reason for this blog:↵
I have used this trick for a somewhat long time, but it seems that not many programmers are aware of this method (+ I didn't find anything talking about this technique), so here it is :)↵
↵
↵
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.↵
↵
The idea is to use pointer casting.↵
↵
Let's say we want to use pair<int,int> with an 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<long long>, 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 integers to use. Is there an easier way that is able to store any data structure?↵
↵
Luckily there is!↵
↵
We can use bitsets, and resize them as we wish.↵
Following our previous example:↵
↵
```↵
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;↵
```↵
↵
Here we create a bitset exactly the size of our class, making us able to use any standard container with our pair<int,int>.↵
↵
Reason for this blog:↵
I have used this trick for a somewhat long time, but it seems that not many programmers are aware of this method (+ I didn't find anything talking about this technique), so here it is :)↵
↵
