Cool C++0X features XIV: Initializer lists

We talked last time about ranged fors and how they can simplify our life in C++0x. Now we are going to take a trip back to old C land. Remember when you could initialize your arrays like this:

int v[] = {1, 2, 3, 4};

C++0X brought a lot of changes to the world, and suddenly instead of int[] you were supposed to use vector, and with it your initializer didn't work anymore. Though luck. Try to compile this:

#include <vector>
int main() {
	std::vector<int> v = {1,2,3,4};
	return 0;
}

If you did compile it with g++, you may have noticed an interesting error message:

error: in C++98 ‘v’ must be initialized by constructor, not by ‘{...}’
warning: extended initializer lists only available with -std=c++0x or -std=gnu++0x

That's interesting. Try to compile it with g++ again, but using C++0x instead of plain C++. Magic, now it works!

Initializers lists bring the best of C to C++ world (?) by letting you use initialize any object with an initializer. And I mean *any* object, not just vectors. For example, say you have a map (a map and a bunch of other stuff):

int main() {
	map<string, vector<int>> v = {
			{ "a", {1,2,3} },
			{ "b", {4,5,6} },
			{ "c", {7,8,9} }
		};

	cout << v["b"][1] << "n";
	return 0;
}

Yes, that works! Maps, vectors, pairs, and even your own custom objects, but we'll see that next time.