C++ 11通过引用函数传递可变数量的对象

Question

我试图在 C++11 中通过引用传递可变数量的对象。

可变参数网络的 C 风格看起来不是很优雅，所以我尝试使用 std::initialiszer_list。

但是我找到的所有例子都是通过复制传递的，我写了一个简单的例子来说明我想要实现的目标:

//Example class for illustration purposes
class MyClass
{
public:
    MyClass()
    : m_id(0), m_idChecks(0)
    {}
    ~MyClass(){}

    int getId()
    {
        m_idChecks++;
        return m_id;
    }
    int getIdChecks() const
    {
        return m_idChecks;
    }

private:
    int m_id;
    int m_idChecks;
};


// I want to do something like this (pass the objects by reference):
// void test_initializerList(std::initializer_list<MyClass&> listClasses) 
// But only pass by copy works:
void test_initializerList(std::initializer_list<MyClass> listClasses) 
{
    // Doing operations on copies of the object:
    int sum = 0;
    for(auto c : listClasses)
    {
        sum += c.getId();
    }
    std::cout << "\n id: " << sum;
}
void test()
{

    MyClass c1;
    MyClass c2;
    MyClass c3;

    test_initializerList({c1,c2,c3});
    std::cout << "\n Wanted: " << 1 << " id checks, got: " << c1.getIdChecks() << "\n";
}

那么在现代 C++ 中如何传递可变数量的参数呢？示例表示赞赏!

Answer 1

不幸的是，initializer_list 只能复制它的参数，不能保存对它的引用(至少是直接引用)。但是，有解决方法(示例已修剪):

#include <initializer_list>
#include <iostream>
#include <functional>

//Example class for illustration purposes
class MyClass
{
public:
    MyClass() : m_idChecks(0) {}
    ~MyClass(){}

    int getId() const
    {
        return m_idChecks++;
    }
    int getIdChecks() const
    {
        return m_idChecks;
    }

private:
    mutable int m_idChecks;
};


using r = std::reference_wrapper<MyClass>;
void test_initializerList(std::initializer_list<r> listClasses) 
{
    // Doing operations on copies of the object:
    int sum = 0;
    for(const auto& c : listClasses)
    {
        sum += c.get().getId();
    }
}
int main()
{

    MyClass c1;
    MyClass c2;
    MyClass c3;

    test_initializerList({c1,c2,c3});
    std::cout << "\n Wanted: " << 1 << " id checks, got: " << c1.getIdChecks() << "\n";
}