per_platform

def per_platform(linux_arm64: '_T | None' = None, linux_x86_64: '_T | None' = None, macos_arm64: '_T | None' = None, macos_x86_64: '_T | None' = None) -> None: ...

An object containing differing homogeneous platform-dependent values.

The values should be evaluated for the execution environment, and not the host environment (I.e. it should be evaluated in a rule which requests Platform).

Expected usage is roughly:

class MyFieldType(...):
    value = str | per_platform[str]

    @classmethod
    def compute_value(  # type: ignore[override]
        cls,
        raw_value: Optional[Union[str, per_platform[str]]],
        address: Address,
    ) -> Optional[Union[str, per_platform[str]]]:
        if isinstance(raw_value, per_platform):
            # NOTE: Ensure the values are homogeneous
            raw_value.check_types(str)

        return raw_value

...

@rule
async def my_rule(..., platform: Platform) -> ...:
    field_value = target[MyFieldType].value

    if isinstance(field_value, per_platform):
        field_value = field_value.get_value_for_platform(platform)

    ...

NOTE: Support for this object should be heavily weighed, as it would be inappropriate to use in certain contexts (such as the source field in a foo_source target, where the intent is to support differing source files based on platform. The result would be that dependency inference (and therefore the dependencies field) wouldn't be knowable on the host, which is not something the engine can support yet).