I was trying to define a custom hash function so that I can use my class inside unordered_sets and unordered_maps but I am facing the above error and I dont know what this means.
I have managed to replicate the error with the following MCVE.
#include <unordered_set>
class A {
int num;
public:
A(int num) : num(num) {}
int getNum() const { return num; }
bool operator==(const A& other) const { return num == other.getNum(); }
};
namespace std {
template<>
struct hash<A> {
size_t operator()(const A& key) {
return key.getNum();
}
};
}
int main() {
std::unordered_set<A> mySet;
mySet.emplace(1);
return 0;
}
I dont understand what this error is all about since I learned about defining custom hash function very recently and this is my first time doing so. I have used the method described here to learn how to define custom hash functions. I tried removing all the const since I felt that might be the cause of this problem but it led to other problems.
Here is the 3 errors the above code gives in Visual Studio 2022.
Can someone kindly explain to me what is going on here and how do I define the hash function properly.
