feat: add startsWith and endsWith

[jly36963]

No description provided.

[jly36963]

Wishing for a more succinct way to express this type, but position creates a bunch of extra if/else blocks and corner cases

[gustavoguichard]

Is positioning part of the native API? I didn't know about it.
In this case I think you can use Slice in to simplify the type implementation

[jly36963]

It is, but the way startsWith and slice handle negative indices is a little different

[jly36963]

[jly36963]

I tried to capture all these cases in the unit tests

[gustavoguichard]

Suggested change

	? P extends 0
	? T extends `${infer TFirst}${infer TRest}`
	? S extends `${infer SFirst}${infer SRest}`
	? TFirst extends SFirst
	? StartsWith<TRest, SRest, P> // Compare next character
	: false // T differs from S
	: true // S (Search) is exhausted (and didn't fail)
	: false // T (Text) is exhausted with S (Search) leftover
	: StartsWith<Slice<T, P>, S, 0> // P is >0, slice
	? Slice<T, P> extends `${S}${string}` ? true : false

[jly36963]

Oooooh I forgot that TS could do

`${S}${string}`

[jly36963]

Your suggestion won't work as-is because of the way startsWith handles negative position, but with a little bit of adaptation I can replace the existing type with something a bit shorter

[gustavoguichard]

Go on and implement endsWith along with it 😉

[jly36963]

Go on and implement endsWith along with it 😉

endsWith might need to wait until we figure out the negative index issue with slice. endsWith has a position param (endPosition) that might make things complicated with slice

I'll start a second PR with it if I can make it work. (PR on this branch, or on main if you accept/merge this one.)

[gustavoguichard]

I believe you can use Slice<S, 0, P> to implement endsWith, can't you?

You probably wouldn't need the negative as it is done here

[gustavoguichard]

@jly36963 I just merged the fix for slice and it now accepts negative indexes

[gustavoguichard]

Could you keep alphabetical order here? I think it is the only place where it was overlooked.

[jly36963]

@jly36963 I just merged the fix for slice and it now accepts negative indexes

False alarm on my part -- negative indices will always return false for endsWith. I didn't have to worry about forwarding negative indices to Slice

The behavior for out-of-bounds indices and negative indices are opposite for startsWith/endsWith. You'll notice this if you look at the tests for each.

[gustavoguichard]

LGTM