Well, I wrote the code for this a while back, and although it was originally intended as a replacement for just std.json (thus the repo name), it does have the framework in place to be a generalized serialization framework, and there is the start of xml, and bson implementations, so I'm releasing it as std.serialization. The JSON implementation is the only one I'd consider ready for production use however. The (de)serialization framework takes a step back and asks, "Why do we need pull parsers?", the answer to which is that allocations are slow, so don't allocate. And that's exactly what I do. The serializer does absolutely *no* allocations of it's own (except for float->string conversion, which I don't understand the algorithms enough to implement myself) even going so far as to create an output range based version of to!string(int/uint/long/ulong/etc.). And the benefits of doing it this way are very clearly reflected in the pure speed of the serializer. On my 2ghz i5 Macbook Air, it takes 50ms to serialize 100k objects with roughly 600k integers contained in them when compiled with DMD, this roughly half the time it takes to generate the data to serialize. Compile it with GDC or LDC and that time is cut in half. I have done the exact same thing with deserialization as well, the only allocations done are for the output objects, because there is no intermediate representation.
So how do I use this greatness? Simple! import std.serialization, and apply the @serializable UDA to the class/struct you want to serialize, then call toJOSN(yourObject) and fromJSON!YourType(yourString) to your heart's content!
Now, there are other serialization libraries out there, such as orange, that take the compile-time reflection approach, but the amount of code required to implement a single format is just massive 2100 lines for the XMLArchive. The entire JSON (de)serialization, which *includes* both the lexer and parser is only 900 lines.
Wow, that went a bit more towards a salesman-like description than I as aiming for, so I'll just end this here and give you the link, before this ends up looking like a massive, badly written, sales pitch :D
https://github.com/Orvid/JSONSerialization