What would a std::map extended initializer list look like?

I'd like to add to doublep's answer that list initialization also works for nested maps. For example, if you have a std::map with std::map values, then you can initialize it in the following way (just make sure you don't drown in curly braces):

int main() {
    std::map<int, std::map<std::string, double>> myMap{
        {1, {{"a", 1.0}, {"b", 2.0}}}, {3, {{"c", 3.0}, {"d", 4.0}, {"e", 5.0}}}
    };

    // C++17: Range-based for loops with structured binding.
    for (auto const &[k1, v1] : myMap) {
        std::cout << k1 << " =>";
        for (auto const &[k2, v2] : v1)            
            std::cout << " " << k2 << "->" << v2;
        std::cout << std::endl;
    }

    return 0;
}

Output:

1 => a->1 b->2
3 => c->3 d->4 e->5

Code on Coliru