On Mon, Jan 10, 2022 at 3:49 AM Christopher Barker <pythonchb@gmail.com> wrote:
> > If "x->y" is syntactically valid anywhere in Python code, it's not a
> problem that there are no core data types for which it's meaningful.)
>
> Here's where I'm not so sure -- this looks a lot like a binary operator, but it behaves quite differently. IIUC it would always create a Callable, regardless of what the types were of the two other types. And it would not invoke a dinder on either, yes.
>
> Nor would it be like assignment.
>
> This is even worse than the use of [] in type hinting which is also using the same sytax for a very different meaning -- at least that one is stil calling __getitem__ :-)
>
From my understanding, "x->y" would create a Callable if given two
*types*, but its meaning if given two other objects is still
undefined. So there's still room for it to be an operator, just like
[] is, and for it to be given semantic meaning for the 'type' type and
all of its subclasses. Or alternatively, there's room for it to be
given meaning in a completely different way, but still universally
(there's a proposal for it to be a form of inline function, although
I'm not 100% sure of the details there).
With the current iteration of PEP 677, `(x) -> y` would return a special object (defined in the `types` module) that simply holds whatever `x` and `y` evaluate to. You could put whatever expression you want at runtime and it would work, though a static checker may be unhappy with you.
ChrisA
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