How to construct an std::array with index sequence?

Question

How can I construct an std::array with an index sequence, or a lambda which depends on a sequential index?

std::iota and std::generat

Answer 1

The next approach should work for you:

template
constexpr auto create_array_impl(std::index_sequence) {
    return std::array{ {I...} };
}

template
constexpr auto create_array() {
    return create_array_impl(std::make_index_sequence{});
}

You can create an array like:

constexpr auto array = create_array();

wandbox example

One can modify the aforementioned solution to add a lambda in the next way:

template
constexpr auto create_array_impl(F&& func, std::index_sequence) {
    return std::array{ {func(I)...} };
}

template
constexpr auto create_array(F&& func) {
    return create_array_impl(std::forward(func), std::make_index_sequence{});
}

And then use:

const auto array = create_array([](auto e) {
    return e * e;
});

wandbox example