How to specify any/unknown/variant type in GDScript?

Question

Is there a way to specify an unknown type in GDScript?

GDScript docs use the type Variant for this (for example in Array.count method).

Say, I'd like to write an identity function. I can do it like so:

func identity(x):
    return x

But I'd like to declare that both the parameter type and return value could be anything. Something like:

func identity(x: Variant) -> Variant:
    return x

This doesn't work though. Variant is not a known type name. I tried various names, bot nothing seems to work.

Is the only option to leave off the type?