A part of the Standard Library (C++).

std::vector v = {1, 2, 3};

{1, 2, 3} in the code above is an example of an std::initializer_list.

#include<initializer_list>

class Vector {
    Vector(std::initializer_list<double> list) : elements_(new double[list.size()]), size(list.size()) {
        std::copy(list.begin(), list.end(), elements);
    }
}

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