Fails to compile when asked to serialize a struct that contains a char array

[marlowa]

Here is the code:

`#include <alpaca/alpaca.h>

struct StartPacket
{
int32_t byteCount;
char magic[4];
};

int main()
{
StartPacket startPacket;
std::vector<uint8_t> buffer;
auto size = alpaca::serialize(startPacket, buffer);
return 0;
}
`

and here is the compilation error:

In file included from thirdparty/alpaca/include/alpaca/alpaca.h:9, from serialise.cpp:1: thirdparty/alpaca/include/alpaca/detail/struct_nth_field.h: In instantiation of ‘constexpr decltype(auto) alpaca::detail::get(type&) [with long unsigned int index = 0; type = const StartPacket&; long unsigned int arity = 5]’: thirdparty/alpaca/include/alpaca/alpaca.h:137:60: required from ‘void alpaca::detail::serialize_helper(const T&, Container&, std::size_t&) [with alpaca::options O = alpaca::options::none; T = StartPacket; long unsigned int N = 5; Container = std::vector<unsigned char>; long unsigned int I = 0; std::size_t = long unsigned int]’ thirdparty/alpaca/include/alpaca/alpaca.h:169:62: required from ‘std::size_t alpaca::serialize(const T&, Container&) [with T = StartPacket; long unsigned int N = 5; Container = std::vector<unsigned char>; std::size_t = long unsigned int]’ serialise.cpp:13:54: required from here thirdparty/alpaca/include/alpaca/detail/struct_nth_field.h:54:11: error: 5 names provided for structured binding 54 | auto &[p1, p2, p3, p4, p5] = value; | ^~~~~~~~~~~~~~~~~~~~ thirdparty/alpaca/include/alpaca/detail/struct_nth_field.h:54:11: note: while ‘const StartPacket’ decomposes into 2 elements In file included from serialise.cpp:1: thirdparty/alpaca/include/alpaca/alpaca.h: In instantiation of ‘void alpaca::detail::serialize_helper(const T&, Container&, std::size_t&) [with alpaca::options O = alpaca::options::none; T = StartPacket; long unsigned int N = 5; Container = std::vector<unsigned char>; long unsigned int I = 0; std::size_t = long unsigned int]’: thirdparty/alpaca/include/alpaca/alpaca.h:169:62: required from ‘std::size_t alpaca::serialize(const T&, Container&) [with T = StartPacket; long unsigned int N = 5; Container = std::vector<unsigned char>; std::size_t = long unsigned int]’ serialise.cpp:13:54: required from here thirdparty/alpaca/include/alpaca/alpaca.h:137:20: error: ‘void field’ has incomplete type 137 | decltype(auto) field = detail::get<I, decltype(ref), N>(ref); | ^~~~~

This seems like a bug to me. This is with the latest alpaca code via git clone as of 2024-12-28.

[lrodorigo]

struct StartPacket
{
int32_t byteCount;
std::array<char,4> magic;
};

and it is just working.

[marlowa]

Thank you for your reply. Using std::array instead of old style C arrays is obviously much better. However, I think that something has to change. Either alpaca is changed so that the use of C arrays works (i.e. fix that compilation error), or alpaca documentation needs to say that C arrays are not supported and std::array should be used instead.