call_n_times.cpp

#include <iostream>
#include <array>
#include <cassert>
using namespace std;

constexpr int f()
{
    return 42;
}

int g()
{
    static int cnt;
    return ++cnt;
}

template<typename T, std::size_t ... Is>
constexpr array<int, sizeof...(Is)> helper(T f, index_sequence<Is...>)
{
    return array<int, sizeof...(Is)> { ((void)Is, f())... };
}

template<int N, typename T>
constexpr auto create_int_arr_with_length_n(T f) -> array<int, N>
{
    return helper(f, make_index_sequence<N>());
}

int main()
{
    constexpr auto arr = create_int_arr_with_length_n<10>(f);
    static_assert(arr.size() == 10, "");
    static_assert(arr[9] == 42, "");
    auto a2 = create_int_arr_with_length_n<10>(g);
    assert(a2.size() == 10);
    assert(a2[5] == 6);
}