I don t understand why `lastEndTokenIndex` is ` 1` neutral f

Question

I don t understand why `lastEndTokenIndex` is ` 1` neutral face If I use `lastIndexOf` without `fromIndex` than the result is the expected 40 But 40 is bigger than 0 so this fromIndex shouldn t interfere with the result should it ```fun main val sb = StringBuilder lt products gt lt product gt 2 lt product gt lt product gt 4 lt product gt lt products gt val endToken = lt product gt val fromIndex = 0 val lastEndTokenIndex = sb lastIndexOf endToken fromIndex println lastEndTokenIndex $lastEndTokenIndex ``` Kotlin Playground <https pl kotl in SlHzdIq1j>

karelpeeters · Answer

It starts looking back from `fromIndex`

Stephan Schroeder · Answer

so how do I tell it that it can stop looking backwards because it s guaranteed not to be at the start of the string because i already checked the start of the stringbuilder in an earlier iteration

karelpeeters · Answer

I don t understand what you actually want to find All indices The first one The last one

Stephan Schroeder · Answer

i m looking for the last index that is bigger than fromIndex

karelpeeters · Answer

Then just do `lastIndexOf` and check if the result is indeed larger than `fromIndex`

Stephan Schroeder · Answer

yes that works but it s inefficient because in the real code the stringbuilder is created in a loop so the start everything before fromIndex is already guaranteed to not contain endToken

Ruckus · Answer

Then write your own function

Stephan Schroeder · Answer

done sunglasses ```fun StringBuilder lastIndexOfAfter str String startIndexOrAfter Int Int tailrec fun lastIndexOfAfter lastIndexFound Int sb StringBuilder str String fromIndex Int Int val foundIndex = sb indexOf str fromIndex if foundIndex== 1 return lastIndexFound else return lastIndexOfAfter foundIndex sb str foundIndex+1 return lastIndexOfAfter 1 this str startIndexOrAfter ```

karelpeeters · Answer

And can t you just look in the newly appended string instead

karelpeeters · Answer

Or what are you doing with the buffer

Stephan Schroeder · Answer

nope because the string i m looking for might have been created when the new chunk was appended it was seperated before

Stephan Schroeder · Answer

But my extension function seems to work and I even used `tailrec` in it so I m feeling pretty good right now sunglasses

Stephan Schroeder · Answer

in case somebody is interested in checking it out in the playground <https pl kotl in HMmaz6g3F>

Stephan Schroeder · Answer

i guess this way less cooler implementation no tailrec pensive is superior in terms of readability and performance ```fun StringBuilder lastIndexOfAfter2 str String startIndexOrAfter Int Int for index in this length str length downTo startIndexOrAfter if this startsWith str index return index return 1 ```