Julia's burgeoning popularity has renewed my interest in dynamic dispatch.
It seems to me that many methods that have been written as a giant switch
on types can more clearly be written using dynamic dispatch. It was
prettty exciting to see that Python already has single dispatch built in,
and that it supports type annotations!
Would it be possible and desirable to extend it slightly to support Union
types?
---
In [1]: from functools import singledispatch
In [3]: from typing import Any, Union
In [4]: @singledispatch
...: def a(x: Any):
...: print("a")
...:
In [5]: class X: pass
In [6]: class Y: pass
In [7]: @a.register
...: def _(x: Union[X, Y]):
...: print("b")
...:
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-7-b6a194bcade0> in <module>
1 @a.register
----> 2 def _(x: Union[X, Y]):
3 print("b")
4
~/.pyenv/versions/3.8.5/lib/python3.8/functools.py in register(cls, func)
858 argname, cls = next(iter(get_type_hints(func).items()))
859 if not isinstance(cls, type):
--> 860 raise TypeError(
861 f"Invalid annotation for {argname!r}. "
862 f"{cls!r} is not a class."
TypeError: Invalid annotation for 'x'. typing.Union[__main__.X, __main__.Y]
is not a class.
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