Why can’t simple initialize (with braces) 2D std::array? [duplicate]

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std::array<T, N> is an aggregate that contains a C array. To initialize it, you need outer braces for the class itself and inner braces for the C array:

std::array<int, 3> a1 = { { 1, 2, 3 } };

Applying this logic to a 2D array gives this:

std::array<std::array<int, 3>, 2> a2 { { { {1, 2, 3} }, { { 4, 5, 6} } } };
//                                   ^ ^ ^ ^            ^ ^
//                                   | | | |            | |
//                                   | +-|-+------------|-+
//                                   +-|-+-|------------+---- C++ class braces
//                                     |   |
//                                     +---+--- member C array braces

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