Overload resolution in C++

In Page 562 The C++ Programming Language 4e, the author shows two functions:

char& operator[](int n) {}char operator[](int n) const {}

If I write

char c = someObj[2];

Since the resolution didn't take care of the return type, and then, which function will be chosen?

I made several tries and it just to call char& operator[](int n) {}, and I think the const function defined here just to give it a chance to be able to be called in some context that require a const. But I not quite sure that.

this is my testing code:

#include <iostream>using namespace std;class A {private:    char p[10] = "abcdefg";public:    char operator[](int n) const {        cout << "const function"<< endl;        return p[n];    }    char& operator[](int n) {        cout << "plain function"<< endl;        return p[n];    }};int main() {    A a;    a[2];    const char &c = a[4];}