Emplacement of a vector with initializer list

The previous answer mentioned you could get the code to compile when you construct the vector in line and emplace that. That means, however, that you are calling the move-constructor on a temporary vector, which means you are not constructing the vector in-place, while that's the whole reason of using emplace_back rather than push_back.

Instead you should cast the initializer list to an initializer_list, like so:

#include <vector>
#include <initializer_list>

int main()
{
    std::vector<std::vector<int>> vec;
    vec.emplace_back((std::initializer_list<int>){1,2});
}

Template deduction cannot guess that your brace-enclosed initialization list should be a vector. You need to be explicit:

vec.emplace_back(std::vector<double>{0.,0.});

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Note that this constructs a vector, and then moves it into the new element using std::vector's move copy constructor. So in this particular case it has no advantage over push_back(). @TimKuipers 's answer shows a way to get around this issue.