Support `Generic` structs

Hi! Is it possible to add support for generics ?

Example:

from typing import TypeVar, Generic, Any

import msgspec


T = TypeVar("T", bound=Any)


class MyStruct(msgspec.Struct, Generic[T]):
    value: T


decoder = msgspec.json.Decoder(MyStruct[int])

assert decoder.decode(b'{"value": 1}').value == 1

If I understand correctly, at the moment the only way to create a generic structure is to use type():

def GenericStruct(type_: Type) -> Type[msgspec.Struct]:
    return type(  # type: ignore
        "MyStruct",
        (msgspec.Struct,),
        {
            "__annotations__": {
                "value": type_,
            },
        }
    )


decoder = msgspec.json.Decoder(GenericStruct(int))

assert decoder.decode(b'{"value": 1}').value == 1

[jcrist]

Is this somewhere on the roadmap to be implemented?

This is definitely something that’s in scope, and that I want to support. It’s just not done yet. msgspec is a side hobby project for me, so features only get added when I have free time. I can’t give you an estimate on when this will be resolved, but hopefully sometime in the next few months.

[tijs2]

I am looking for the same functionality because I want to inherit a base class:

It is not the nicest example but the idea is like this:

class Base(msgspec.Struct, Generic[T]):
     id: int
     value: T

class Car(Base[str]):
    extra_variable_car: int

class Bike(Base[int]):
    extra_variable_bike: int

This means I can attach new fields in the subclass and use the ones from the parent class. But also assume there is always a value field but the type could change which can be checked by Mypy if I create a certain object instance.

Is this somewhere on the roadmap to be implemented?