修改 std::map 的键 [英] Modify key of std::map

问题描述

有没有办法修改 std::map 或 ?这个例子 显示了如何通过重新平衡树来做到这一点.但是，如果我提供一些密钥不需要重新平衡的保证怎么办?

Is there a way to modify the key of a std::map or ? This example shows how to do so with rebalancing the tree. But what if I provide some guarantees that the key won't need to be rebalanced?

#include <vector>
#include <iostream>
#include <map>


class Keymap
{
private:    
    int key; // this key will be used for the indexing
    int total;
public:
    Keymap(int key): key(key), total(0)
    {}
    bool operator<(const Keymap& rhs) const{
        return key < rhs.key;
    }
    void inc()
    {
        total++;
    }
};
std::map<Keymap, int> my_index;



int main (){
    std::map<Keymap, int> my_index;
    Keymap k(2);
    my_index.insert(std::make_pair(k, 0));

    auto it = my_index.begin();

    it->first.inc(); // this won't rebalance the tree from my understanding
    return 0;
}

由于it->first

有什么办法可以覆盖这种行为吗?

Is there any way to override this behavior?

推荐答案

You can make inc const and total mutable

You could make inc const and total mutable

class Keymap
{
private:    
    int key; // this key will be used for the indexing
    mutable int total;
public:
    Keymap(int key): key(key), total(0)
    {}
    bool operator<(const Keymap& rhs) const{
        return key < rhs.key;
    }
    void inc() const
    {
        total++;
    }
};

但是你确实需要问问自己为什么要这样做，mutable 用得不多.

But you do need to ask yourself why you are doing this, mutable isn't used much.

您说得对，不会发生再平衡.

You're right that no rebalancing is going to happen.

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