C++11/C++14 initializer_list - 2020

"If you're an experienced C++ programmer and are anything like me, you initially approached C++11 thinking, "Yes, yes, I get it. It's C++, only more so." But as you learned more, you were surprised by the scope of the changes. auto declarations, range-based for loops, lambda expressions, and rvalue references change the face of C++, to say nothing of the new concurrency features. And then there are the idiomatic changes. 0 and typedefs are out, nullptr and alias declarations are in. Enums should now be scoped. Smart pointers are now preferable to built-in ones. Moving objects is normally better than copying them.
- Effective Modern C++ by Scott Meyers

When we want to initialize a vector, we had to do the following:

// C++03
std::vector v;
v.push_back(1);
v.push_back(2);
v.push_back(3);
v.push_back(4);

Now, with C++ 11, we can do this:

// C++11
std::vector v = { 1, 2, 3, 4 };

C++11 binds the concept to a template, called std::initializer_list. This allows constructors and other functions to take initializer-lists as parameters:

#include <iostream>
#include <vector>

class MyNumber
{
public:
    MyNumber(const std::initializer_list<int> &v;) {
        for (auto itm : v) {
            mVec.push_back(itm);
        }
    }

    void print() {
	for (auto itm : mVec) {
	    std::cout << itm << " ";
	}
    }
private:
    std::vector<int> mVec;
};

int main()
{
    MyNumber m = { 1, 2, 3, 4 };
    m.print();  // 1 2 3 4

    return 0;
}

C++11/C++14 New Features