如何在 C++ 中对成员数据进行别名？

Question

How to alias pair member-data in C++?

I have a container of std::pair<int,int> to store master-slave pairs.

For better readability I want to use something like:

using Master = std::pair<int,int>::first;

std::pair<int,int> myPair;
auto myMaster = myPair.Master;

What would be the correct syntax here?

Thank you, in advance.

Answer 1

You can name a pointer-to-member

constexpr auto Master = &std::pair<int,int>::first;

std::pair<int,int> myPair;
auto myMaster = myPair.*Master;

Answer 2

An alternative would be to use the tuple-like get access to std::pair with a self-defined constant:

const std::size_t Master = 0;

std::pair<int,int> myPair;
auto myMaster = std::get< Master >( myPair );

Somewhat cleaner and more readable than pointered access IMHO.

Answer 3

I am going with the following:

int main() {
    cout<<"Hello World\n";
    
    constexpr auto Master = &std::pair<int,int>::first;

    std::pair<int,int> myPair;
    std::pair<int,int> myPair2;

    myPair.*Master = 321;
    myPair2.*Master = 10;
    cout<<myPair.*Master;
    cout<<myPair2.*Master;

    return 0;
}

Thanks @ Caleth