[stdlib] Optional start and length arg for String._strref_dangerous

[fknfilewalker]

Normally when one wants to create a truncated StringRef, a ptr to the String together with offsets need to be used. This is annoying and dangerous and could be done more safely during the _strref_dangerous call. This also adds bound guards

[laszlokindrat]

Thanks for the patch! @JoeLoser Do you have thoughts on this?

[JoeLoser]

Thanks for the patch! @JoeLoser Do you have thoughts on this?

In general, use of _strref_dangerous and friends will go away in favor of some of the StringSlice (safe string slice) work going on internally, right? I need to look closer at it before I can give a good review here.

[laszlokindrat]

Thanks for the patch! @JoeLoser Do you have thoughts on this?

In general, use of _strref_dangerous and friends will go away in favor of some of the StringSlice (safe string slice) work going on internally, right? I need to look closer at it before I can give a good review here.

Yeah, although I think this could be useful in the meanwhile, and low risk since it's a hidden API anyway.

@fknfilewalker Could you please rebase after the next nightly, and change this patch to update the potential uses in https://github.com/modularml/mojo/pull/2710 and maybe other places? That would give us a definitive picture of how much this actually helps.

[laszlokindrat]

Thank you! I have a few more requests, but LGTM otherwise!

[laszlokindrat]

Also, can you please update String.{end,start}swith (and any other places you're aware of) to use these?

[fknfilewalker]

Also, can you please update String.{end,start}swith (and any other places you're aware of) to use these?

For now I only checked string.mojo and there are not many places where it is really helpful and since you want to replace it with StringSlice anyway maybe we should just drop this?

[laszlokindrat]

Is it really only one place where it's useful? I would have expected more. If you find one or two more places, I think we should land it, otherwise you're probably right, it's not pulling its weight.