我究竟如何重载“{”运算符？

Question

To initialize an std::vector, I can directly use the initializer_list, like so:

std::vector<int> myVec = {1, 2, 3, 4};

If i create a custom List Class (which will hold a number of items), for example class customVector (for simplicity only with ints, I think I could figure out how to do it with templates myself, if necessary), can I overload the operator '{' in such a way that an instance of customVector can be initialized in the same matter? So that I could write

customVector myCustomVec = {1, 2, 3, 4}

Answer 1

You can accomplish what you ultimately want, but not by overloading any operators – { is not an operator.

vector does this by having a constructor that takes an initializer_list parameter, and you can do the same with your class.

Learning how to do it and implementing it left as an exercise.

Answer 2

You cannot, since { is not an operator. Up to C++20 , the following operators were overridable:

+    -    *    /    %    ^    &    |    ~    !    =
<    >    +=   -=   *=   /=   %=   ^=   &=   |=   <<
>>   >>=  <<=  ==   !=   <=   >=   &&   ||   ++   --
,    ->*  ->   ()   []

C++20 added the spaceship operator <=> but I believe that's it.

Answer 3

As the others have pointed at, { is not an operator. However, you can still use the initializer list as you like. It's a part of the standard library.

#include <iostream>
#include <initializer_list>
using namespace std;

template <typename T>
struct customVector {
    customVector(std::initializer_list<T> list) : size(list.size()) {
        arr = new T[size];
        int count = 0;
        for(auto val: list) arr[count++] = val;
    }
    T* arr;
    std::size_t size;

    ~customVector() {
        for(int i = 0; i < size; i++)
            std::cout << arr[i] << std::endl;
        delete [] arr;
    }
};

int main() {
    customVector<int> myCustomVec = {1, 2, 3, 4};
}