Thanks, that is definitely a downside to the shift operator overloading approach. I'll take that onboard and investigate whether a single operator to handle both would mesh with the current design.
You can just use the boost.pfr technique to iterate fields though.
Or if you want, starting from C++26 and e.g. clang-21: https://gcc.godbolt.org/z/G1TqP3a8P
I'd like to read an even more thorough overview of how it works and all the gotchas before I'd consider using this 'in production' but the API looks very easy to use and very elegant.
EDIT: just hit the section on portability, seems like you would always have to use that API, yeah? I feel like when you are writing network code you simply have to make it portable from the get-go. I guess I'm always thinking about having it run on client machines.
Thanks. The documentation could definitely be fleshed out with some more examples.
You'd likely want to always use that API (or layer something on top of it) unless you're in control of both ends and know they were built with the same toolchain & settings. One area where I've skipped over it is by writing a basic code gen tool (albeit unfinished as most personal projects) that generates the serialisation functions at compile-time from a very basic DSL that describes the network structures (of a game protocol I don't control). If it detects that the current toolchain is going to generate a binary-compatible struct layout and there aren't any variable length fields in there (no strings, basically), it'll generate a memcpy (via using get/put on the stream) rather than per-field (de)serialisation. If it can guarantee alignment of the buffer, which is a tougher requirement to meet, it'll give you a view directly into the network buffer so you effectively have zero-overhead deserialisation. Very much a work in progress but there's scope for making things quite efficient with just a few basic building blocks.
I know it's a convention since the inception of the language, but the operator overload abuse of the bitshift operator still makes me sad every time I see it :(
You are not alone. many on the standard committee are trying to get rid of it. std::print is the new way to do io instead of cout in part so you don't have to abuse shift for io. This is new in c++23 though so few people know about it.
Bjarne appears to prefer cout though, so it isn't universal.
With more complex structures, you need to specify how it should behave. The definition for 'more complex' here is basically no virtual functions, virtual base classes, is trivially copyable and constructible and a few others.
Basically, if it seems like memcpying the structure might be a reasonable thing to do, it'll work. This is why types like std::array will work but std::vector and std::string won't. It can handle those types when inserted individually but not in aggregate since there's no reflection.
The compiler barf does tell the user why it was rejected but... average C++ errors, even with concepts. Not the greatest.
main.cpp:136:52: note: the expression ‘is_trivial_v [with T = UserPacket]’ evaluated to ‘false’
136 | concept pod = std::is_standard_layout_v<T> && std::is_trivial_v<T>;
I'll likely add additional functionality for specifying both operations with a single function since it's been mentioned a few times. Thanks for the repos.
By the way I looked through the code, and had to read about metaprogramming in C++. I wonder why is it so complicated? For example, why constraints like std::is_integral are represented by structs. Doesn't make much sense to me. A function wouldn't be better here?
While this is true, you can do so much these days with functions with 'auto' return types (function templates), constexpr functions/lambdas and "if constexpr"
Sure, auto constexpr stuff can express some things. Not most things though, at least in my experience. Perhaps a skill issue on my part. Or things might have changed again. I'm "still" using C++20 after all.
> What does that mean
Have you ever noticed that the (compile time) "rules" for interacting with templated functions are somewhat different from those of non-templated functions? I don't know if "functions as types" is entirely fair but there is definitely some weirdness.
Practically, it's all through this `type_traits` header that (often) end up in unreadable messes. It's all possible because of the catchy acronym SFINAE. It doesn't make much sense to me either, so I avoid it :)
This looks very cool. Based on the examples, you might like XDR.
It’s far better than the other binary serialization protocols I’ve looked at / implemented. NFSv3 uses it, and it is compatible with a lot of the tricks you play, like in-place endian translation, branch avoidance, zero allocation use cases, etc:
These days, whenever i read "headet only" i immediately get scared about compile times. Does using this library make compilation expensive in the way that eg protobuf or nlohmann_json do?
I don't use the amalgamated version, though (that only exists for this standalone version) and the library overall is significantly smaller than either of those and doesn't drag in nearly as many standard library headers.
Agreed but just to clarify, Hexi sits at a level below something like MessagePack because it doesn't impose any particular encoding on you since the use-case was handling arbitrary binary protocols that you might not have any control over. You could build support for MessagePack on top of Hexi but not the other way around. They're all very different use-cases.
incidentally, the block allocator implementation fails to properly account for alignment requirements:
since the underlying storage is std::array<char, ...>, it's alignment may be less that the required alignment of the requested type and that of the pointers being stored in the free list.
Correct but it doesn't claim to be zero-copy overall. Apologies if it was misleading. In the README, zero-copy is mentioned in context of using view() and span() to obtain views into the buffer, which does allow for it. Very much a "there be dragons but if you're sure..." feature but it's there as an option.
I've also built some tooling on top that makes use of those functions to do zero-copy deserialisation where viable, so it is possible in the right scenarios with a bit of work but it definitely isn't going to always fit.
Consider copying Cereal, which solves this problem by requiring you to create a single templated function ( https://uscilab.github.io/cereal/ )
I'd like to read an even more thorough overview of how it works and all the gotchas before I'd consider using this 'in production' but the API looks very easy to use and very elegant.
EDIT: just hit the section on portability, seems like you would always have to use that API, yeah? I feel like when you are writing network code you simply have to make it portable from the get-go. I guess I'm always thinking about having it run on client machines.
You'd likely want to always use that API (or layer something on top of it) unless you're in control of both ends and know they were built with the same toolchain & settings. One area where I've skipped over it is by writing a basic code gen tool (albeit unfinished as most personal projects) that generates the serialisation functions at compile-time from a very basic DSL that describes the network structures (of a game protocol I don't control). If it detects that the current toolchain is going to generate a binary-compatible struct layout and there aren't any variable length fields in there (no strings, basically), it'll generate a memcpy (via using get/put on the stream) rather than per-field (de)serialisation. If it can guarantee alignment of the buffer, which is a tougher requirement to meet, it'll give you a view directly into the network buffer so you effectively have zero-overhead deserialisation. Very much a work in progress but there's scope for making things quite efficient with just a few basic building blocks.
Bjarne appears to prefer cout though, so it isn't universal.
On US layout colon is a single keypress but < is shift+.
This may explain the discrepancy.
—- from someone who read Bjarne at 16yo. All hail the Bjarne
Array programming languages smugly enter the chat
I tried adding std::string to the UserPacket (from the README)
and the compilation fails - https://onlinegdb.com/B_RJd5UwsBasically, if it seems like memcpying the structure might be a reasonable thing to do, it'll work. This is why types like std::array will work but std::vector and std::string won't. It can handle those types when inserted individually but not in aggregate since there's no reflection.
The compiler barf does tell the user why it was rejected but... average C++ errors, even with concepts. Not the greatest.
main.cpp:136:52: note: the expression ‘is_trivial_v [with T = UserPacket]’ evaluated to ‘false’ 136 | concept pod = std::is_standard_layout_v<T> && std::is_trivial_v<T>;
https://github.com/eliasdaler/MetaStuff
Another take on the same idea with even simpler interface:
https://github.com/apankrat/cpp-serializer
> What does that mean
Have you ever noticed that the (compile time) "rules" for interacting with templated functions are somewhat different from those of non-templated functions? I don't know if "functions as types" is entirely fair but there is definitely some weirdness.
https://en.cppreference.com/w/cpp/language/sfinae
It’s far better than the other binary serialization protocols I’ve looked at / implemented. NFSv3 uses it, and it is compatible with a lot of the tricks you play, like in-place endian translation, branch avoidance, zero allocation use cases, etc:
https://www.rfc-editor.org/rfc/rfc1014
It can generate efficient JS and C++ from a simple YAML file.
I don't use the amalgamated version, though (that only exists for this standalone version) and the library overall is significantly smaller than either of those and doesn't drag in nearly as many standard library headers.
But soon you’ll be bitten by the fact you don’t have a schema and so you’ll move to something like Protobuf or the more efficient FlatBuffers
since the underlying storage is std::array<char, ...>, it's alignment may be less that the required alignment of the requested type and that of the pointers being stored in the free list.
I've also built some tooling on top that makes use of those functions to do zero-copy deserialisation where viable, so it is possible in the right scenarios with a bit of work but it definitely isn't going to always fit.
I would have liked a different froggy reaction for each section but the project budget was zero. :^)