Different behavior between const and readonly for multidimensional array access/strict null checking about typescript HOT 7 CLOSED

• I was unable to test this on prior versions because I'm using TS Playground

Especially on the playground it's easy to test this on prior versions because the playground has a version selector on the top left.

from typescript.

Strangely, this doesn't work, either.

This works in 5.5 beta. For more information, see https://devblogs.microsoft.com/typescript/announcing-typescript-5-5-beta/#control-flow-narrowing-for-constant-indexed-accesses

from typescript.

• I was unable to test this on prior versions because I'm using TS Playground

Especially on the playground it's easy to test this on prior versions because the playground has a version selector on the top left.

I was unaware of that. Thanks for letting me know. I tested it back a few versions and they all produce the same errors.

from typescript.

This is working as intended. A readonly reference doesn't guarantee that the underlying object isn't mutated. I just guarantees that it isn't mutated through that reference. You need to store the value of arrayAccessors[0] in a const local to get the desired behavior.

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function itsaFunction(arrayAccessors: readonly number[])
{
	let someArray: Array<Array<Array<number | null> | null> | null> = new Array<Array<Array<number | null> | null> | null>();

	const arrAcc1 = arrayAccessors[0];
	const arrAcc2 = arrayAccessors[1];

	if (someArray[arrAcc1] !== null && someArray[arrAcc1][arrAcc2] != null)
 		console.log(arrayAccessors);
}

Strangely, this doesn't work, either. Gives the same error.

from typescript.

Strangely, this doesn't work, either.

This works in 5.5 beta. For more information, see https://devblogs.microsoft.com/typescript/announcing-typescript-5-5-beta/#control-flow-narrowing-for-constant-indexed-accesses

Thanks for the info. Good to know this is at least being addressed.

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This issue has been marked as "Working as Intended" and has seen no recent activity. It has been automatically closed for house-keeping purposes.

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