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by pid-1
641 days ago
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Sorry, I could not grok the difference, even after reading a few Rust examples. def foo(int | None = None) ... ... just means the variable's default value is None in a function definition. But it could be either in an actual function call. |
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Say you wanted to define some function taking `YYMMDD | MMDDYY`. If both YYMMDD and MMDDYY are just aliases to `str`, then you gain no information, you cannot discriminate on which one it is, since the union `str | str` just reduces to `str`.
Sum types are disjointed unions, you can't just say `str | str`, the terms are wrapped in unique nominal data constructors, like:
enum Date { MMDDYY(String), YYMMDD(String) }
Then when accepting a `Date` you can discriminate which format it's in. You could do the same in Python by defining two unique types and using `MMDDYY | YYMMDD`.