C++在赋值类变量时使用大括号

Question

当我在C++中声明一个数组时,我可以像这样使用大括号:

int var[3] = {1, 2, 3};

我可以在类中使用大括号声明,比如运算符重载吗？我的意思是,像这样:

class example
{
private:
    int m_sum;
public:
    void operator{}(int a, int b, int c)
    {
        m_sum = a+b+c;
    }
    int get_sum()
    {
        return m_sum;
    }
}

int main()
{
    example ex = {1, 2, 3};
    std::cout << ex.get_sum() << endl; // prints 6
    return 0;
}

上面的代码只是我的想象,但我想使用大括号作为此代码.

Answer 1

You might want a constructor taking an std::initializer_list :

#include <iostream>
#include <algorithm>
#include <initializer_list>

class example
{
private:
    int m_sum;
public:
    example(std::initializer_list<int> parameters)
    {
        m_sum = std::accumulate(std::begin(parameters), std::end(parameters), 0);
    }

    int get_sum() const
    {
        return m_sum;
    }
};

int main() {
    example e = { 1, 2, 3, 4 };
    std::cout << e.get_sum();
}

Live Demo

Another approach is to use a variadic template constructor (I find it less readable, but it has the advantage of making your code generic : you can pass arbitrary elements to the constructor) :

#include <iostream>
#include <algorithm>
#include <initializer_list>

class example
{
private:
    int m_sum;
public:
    template <class... Ts> example(Ts&&... vs) : m_sum(compute_sum(vs...)) { }

    int get_sum() const
    {
        return m_sum;
    }

private:
    template<typename Ts1>
    Ts1 compute_sum(const Ts1& val) { return val; } // termination

    template<typename Ts1, typename... Ts>
    Ts1 compute_sum(const Ts1& arg1, const Ts&... args)
    {
        return arg1 + compute_sum(args...); 
    }
};

Live Demo

Note:

There is no operator{} in C++.