Modify value in unordered_set

Question

I have the following structure:

struct User 
{
    string name;
    bool flag;
    int score;

    bool operator==(const User& user) const
    {
        return name == user.name;
    }
}

namespace std {
    template<>
        struct hash<User>
        {
            size_t operator()(const User& user) const
            {
                return hash<string>{}(user.m_nickname);
            }
        };
}

After that I want to use User with unordered_set container, but after reading another portion of data I want to modify user score\flag etc, therefore it wont affect the hash value, because I know that all users will have unique names beforehand.

In my program I use something like that:

unordered_set<User> set;
while(true)
{    
    User user = *set.find({name});
    user.score++;
}

But after my user object goes out of scope and I find it one more time values remain the same as they were before modifying. How I can solve this problem and maybe I should use other container? I have chosen this one because of O(1) complexity.

Answer 1

In an unordered_set<> each object's value is its key. Hence, the objects can't change.

One way you can get around this is by making the non-key members mutable.

That is, change

bool flag;
int score;

to

mutable bool flag;
mutable int score;

Also, you're modifying a copy.

Change

User user = *set.find({name});

to

auto &user = *set.find({name});