Support Literal type

[CamDavidsonPilon]

👋 what are your thoughts on supporting the Literal type?

[jcrist]

Hmmm, we could definitely make that work. Can you expand a bit on your use case here?

Note that if you're just trying to restrict a field to a smaller set of valid values, you can kind of do this with enums today. Enum types are serialized as strings of their field names, and IntEnum types are serialized as their integer values, so as far as decoders are concerned, these are roughly equivalent:

class Foo(msgspec.Struct):
     x: Literal[1, 2, 3]

class MyEnum(enum.IntEnum):
    a = 1
    b = 2
    c = 3

class Foo2(msgspec.Struct):
    x: MyEnum

msgspec.json.decode(b'{"x": 3}', type=Foo)  # Ok, returns 3 (not implemented currently)
msgspec.json.decode(b'{"x": 3}', type=Foo2)  # Ok, returns MyEnum.c

msgspec.json.decode(b'{"x": 4}', type=Foo)  # Errors, int not in set of valid literals (not implemented currently)
msgspec.json.decode(b'{"x": 4}', type=Foo2)  # Errors, int not in set of valid enum values

[CamDavidsonPilon]

Simply: I have existing types that use Literal:

PdChannel = Literal["1", "2"]

...

class ODReadings(Struct):
    timestamp: str
    od_raw: dict[PdChannel, ODReading]

msgspec.json.decode(..., type=ODReadings) # TypeError: Type 'typing.Literal['1', '2']' is not supported

I could use Enums, but I kinda like literals in this case!

[jcrist]

Cool, yeah, I can definitely add support for this. Adding it to the queue, thanks for the suggestion!

[jcrist]

Thanks for the issue request, this has been fixed in #71. I have a few small fixups I hope to get in before releasing, but feel free to try this out from the main branch if you're interested:

pip install git+https://github.com/jcrist/msgspec

[CamDavidsonPilon]

Already trying it :)

Thanks for devoting time to this, @jcrist!

[jcrist]

This has now been released. Up on pypi now, should be on conda-forge shortly.