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0 points_dain_0y ago0 comments

Don't do this stupid party trick with `global`.

You may as well argue that unit tests are pointless because you could cheat by making the implementations return just the hardcoded values from the test cases.

0 comments

pansa20y ago

This isn't a "party trick" with `global`, it's a fundamental hole in the type system:

    class C:
        def __init__(self) -> None:
            self.i : int | list[int] = 0

        def foo(self) -> None:
            self.i = []
        
        def bar(self) -> int:
            if isinstance(self.i, int):
                self.foo()
                return self.i
            return 0

    print(type(C().bar()))

maleldil0y ago

This seems to work in TypeScript too:

    class C {
        i: number | number[];

        constructor() {
            this.i = 0;
        }

        foo(): void {
            this.i = [];
        }

        bar(): number {
            if (typeof this.i === 'number') {
                this.foo();
                return this.i;
            }
            return 0;
        }
    }

    console.log(typeof new C().bar());

It seems to be a problem with "naked" type unions in general. It's unfortunate.

__MatrixMan__0y ago

Agreed, but I've never found it to be especially problematic. The type checker still catches the vast majority of things you'd expect a type checker to catch.

If you want to be able to change the type of something at runtime, static analysis isn't always going to be able to have your back 100% of the time. Turns out that's a tradeoff that many are willing to make.

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