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Comment by __MatrixMan__ | Hacker News Reader

I'm a bit confused. How can you control how your data is serialized if not manually? Are there languages that use some kind of magically-figures-it-out layer that negotiates the appropriate serialization on the fly?

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Many languages have some kind of macro or codegen system that allows serializing or deserializing based on type definitions. Eg (pseudocode):

    @deriving(json)
    class Person:
      id: int
      name: str

Would give you something like:

    def parse(s: str): Person: ...
    def print(p: Person): str: ...

I see, thanks. I thought maybe we were talking about the choice of json vs something else being automatic and chosen at runtime.

C# (or more precisely .NET libraries) does it using reflection. Attributes let you adjust the behaviour.

Or with build-time source generation (because this specific pattern of reflection is AOT-unfriendly). It's not as convenient if you are using default serializer options, but if you don't - it ties together JsonTypeInfo<T> and JsonSerializerOptions, so it ends up being a slightly terser way to write it. I do prefer the Rust-style serde annotations however.

  record User(string Name, DateOnly DoB);

  [JsonSerializable(typeof(User))]
  partial class SerializerContext: JsonSerializerContext;

  ...
  var user = new User("John", new(1984, 1, 1));
  var response = await http.PostAsJsonAsync(
    url, user, SerializerContext.Default.User);

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