alt Hacker NewsEven with strict flags on, there are failures. A trivial example:
function mutateArray(
arr: (string | number)[]
) {
arr.push(1);
}
const a: string[] = ["one", "two"];
mutateArray(a);
Replies
drzaiusx11 • today at 1:43 PM
Yikes. I've only been using ts for about a year, I had no idea this was considered a "valid" case. Seems like a type error to me. I wonder how they justify this?
teaearlgraycold • today at 9:06 AM
Very interesting. I’m shocked the typescript creators built a system with this failure mode. I guess the solution here is to have tsc change the type of “a” after the call to mutateArray, unless the arr argument is marked as readonly.
Is there a name for this failure mode?
➕ show 4 replies
Woah, that's quite an issue. The equivalent code in Python doesn't typecheck, since `list` is invariant and hence list[str] doesn't fit list[str|int]. Unusual for TS to handle types worse than Python.