Convert std::tuple to std::array C++11

Question

If I have std::tuple (where the type is homogeneous), is there a stock function or constructor to convert to std::array

Answer 1

In C++14 you can do this to generate an array:

auto arr = apply([](auto... n){return std::array{n...};}, tup);

Full code:

#include // apply
#include

//using std::experimental::apply; c++14 + experimental
using std::apply; // c++17

template
auto to_array(Tuple&& t){
    return apply([](auto... n){return std::array{n...};}, t); // c++14 + exp
}

int main(){
    std::tuple t{2, 3, 4};

    auto a = apply([](auto... n){return std::array{n...};}, t); // c++14 + exp
    assert( a[1] == 3 );

    auto a2 = apply([](auto... n){return std::array{n...};}, t); // c++14 + exp
    assert( a2[1] == 3 );

    auto a3 = apply([](auto... n){return std::array{n...};}, t); // c++17
    assert( a3[1] == 3 );

    auto a4 = to_array(t);
    assert( a4[1] == 3 );

}

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Note that the subtle problem is what to do when all types in the source tuple are not the same, should it fail to compile? use implicit conversion rules? use explicit conversion rules?