C++11 passing variadic number of objects by reference to function - c++

Question

I'm trying to pass a variable number of objects by reference in C++11.
The C-style of variadic argumnets did not seem very elegant, so I tried using the std::initialiszer_list.
But all the examples i found used pass by copy, I wrote a simple example of what I want to achieve:
//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";
}
So how do you pass a variable number of arguments in modern C++? Examples are appreciated!

Answer 1

Unfortunately, initializer_list can only copy it's arguments, and can't hold a reference to it (directly at least). However, there is way around it (example trimmed):
#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";
}