Suggestion: NonEmptyArray about type-fest HOT 4 CLOSED

Gotcha. My thinking was more around function arguments:

function Hello(array: NonEmptyArray<string>) {
  /* body */
}

I tend to have a lot of guards in my code that do things like:

if (array.length === 0) {
  return
}

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Sounds very interesting and useful.

On the original discussion thread, they actually propose a different version of it with overloaded map function. The issue is that this type on its own has limited usefulness. Without an actual implementation for a type assertion function (<T>(array: T) => array is NonEmptyArray<T>) one would always end up with a plain array after mapping it.

So this seems a little out of scope for this project.

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Yeah, it just happened yesterday that I needed a type like this. The problem is ergonomics: Where do you get a value of this type from? Imagine an API like this:

function hello(array: NonEmptyArray<string>) {
  /* body */
}

Now you want to use it:

hello(['foo']); // => Works

const arr = ['foo'];
if (arr[0] != null) {
	hello(arr); // => Error
}
if (typeof arr[0] === 'string') {
	hello(arr); // => Error
}
if (arr.length > 0) {
	hello(arr); // => Error
}

So when you use it with a literal or tuple type, this will work fine. But as soon as you have a plain array type this will fail although we have an element or a length check. So there is actually limited purpose of this type alone. To preserve developer ergonomics you actually need to provide a type guard:

function isNonEmptyArray<T>(array: T): array is NonEmptyArray<T> {
	return arr[0] != null;
}

Otherwise every user of this type will have to re-implement this function. But it is currently outside of the scope of this project to provide imlementations like the one above.

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👍

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