How can I initialize an std::array of a class without a default constructor?

Question

Let's say I have a class without a default constructor called Foo<\/code> .

std::vector<Foo> vec(100, Foo(5));

Answer 1

std::array<\/code> is just a thin wrapper around a fixed array. It has no repeat-insert logic, like std::vector<\/code> does. Since Foo<\/code> does not have a default constructor, the only way to initialize an instance of std::array<Foo, N><\/code> is to use aggregate initialization<\/a> with N<\/code> number of values specified (sorry, I know you don't want to to do this), eg:

std::array<Foo, 100> arr{5, 5, 5, ...}; // N times...

Answer 2

With copy constructor, something along these lines:

template <typename T, size_t... Is>
std::array<T, sizeof...(Is)> MakeArrayHelper(
    const T& val, std::index_sequence<Is...>) {
  return {(Is, val), ...};
}

template <typename T, size_t N>
std::array<T, N> MakeArray(const T& val) {
  return MakeArrayHelper<T>(val, std::make_index_sequence<N>{});
}

std::array<Foo, 100> arr = MakeArray<Foo, 100>(Foo(5));