A proof of concept C++20 type-safe variadic argument array creation function (using C++20 Concepts and Variadic Templates)

variadic_param_poc.cpp

#include <array>
#include <iostream>

template<typename ...Args>
constexpr std::size_t ARG_SIZE() { return sizeof...(Args) + 1; }

template<typename From, typename To>
concept SameAs = std::is_same_v<From, To>;

template<std::size_t N, typename T, SameAs<T>... Ts>
constexpr void set(std::array<T, N>& arr, T arg, Ts... args)
{
    static_assert(ARG_SIZE<Ts...>() <= N, "size of args exceeds size of array");

    constexpr std::size_t Idx = N - ARG_SIZE<Ts...>();

    arr[Idx] = arg;
    if constexpr (Idx < N - 1) {
        set(arr, args...);
    }
}

template<typename T, SameAs<T>... Ts>
constexpr std::array<T, ARG_SIZE<Ts...>()> arrayOf(T first, Ts... elements)
{
    auto tmp = std::array<T, ARG_SIZE<Ts...>()>();
    set(tmp, first, elements...);
    return tmp;
}

int main() {
    auto a1 = arrayOf(1, 2, 3); // ok
    auto a2 = arrayOf(1, "a", "b"); // fails requirements

    return 0;
}