C++にpackが欲しい

書きかけ及びパラメータパックの習作
std::formatという安全なsprintfがあるならばP言語のpack/unpackも比較的安全に作れるのでは？という思いつき
(boostのiotreams使えばいいという話もある)

cpp20

#include <iostream>
#include <vector>
#include <cstdint>
#include <cstdlib>
#include <cstring>
#include <string>
#include <type_traits>
#include <concepts>
#include <array>

template<typename T>
concept Serializable = std::copyable<T> && !std::is_pointer_v<T>;

template<Serializable T>
std::vector<uint8_t> _pack(T num){
  std::vector<uint8_t> r(sizeof(num));
  memcpy(r.data(), &num, sizeof(num));
  return r;
}

template<Serializable T, std::integral Tn, Tn m>
std::vector<uint8_t> _pack(T (&n)[m]){
    auto size = sizeof(n);
    std::vector<uint8_t> r(size);
    memcpy(r.data(), n, size);
    return r;
}

template<std::integral T>
struct rev{
    const T &val;
};

template<std::integral T>
std::vector<uint8_t> _pack(rev<T> n){
    auto size = sizeof(T);
    std::vector<uint8_t> r(size);
    auto b = _pack(n.val);
    for(size_t i = 0; i < size; i++){
        r[i] = b[size-i-1];
    }
    return r;
}

std::vector<uint8_t> _pack(std::vector<uint8_t> a){ return a; }

std::vector<uint8_t> _pack(std::string_view s){
  std::vector<uint8_t> r(s.size()+1);
  memcpy(r.data(), s.data(), s.size());
  r[s.size()] = 0;
  return r;
}

template<typename ... T>
std::vector<uint8_t> pack(T ...args){
    std::vector<std::vector<uint8_t>> tmp{ _pack(args)... };
    size_t total_size = 0;
    for(const auto& it : tmp){ total_size += size(it);  }

    std::vector<uint8_t> result(total_size);
    size_t offset = 0;
    uint8_t* ptr = result.data();
    for(const auto& it : tmp){
        memcpy(ptr + offset, it.data(), size(it));
        offset += size(it);
    }
    return result;
}

void display(std::vector<uint8_t> buf){
    printf("length: %zu\n", buf.size());
    for(const uint8_t& b : buf)
      printf("%02X ", b);
    puts("");
}

int main(){
    uint16_t a[] = {1,2,3,4,0xFFEF};
    auto b = pack(std::to_array(a), "1234567", rev<uint32_t>{0x123456}, uint32_t(0x987654));
    display(b);
}