lastIndexOf' with index greater than string length returns Nothing
hdgarrood opened this issue · 4 comments
In the JavaScript API, the fromIndex parameter in str.lastIndexOf(pattern [, fromIndex]), perhaps surprisingly, represents the index at which to stop searching (if we imagine the search proceeds from left-to-right). This means that if you provide a fromIndex which is greater than or equal to the string's length, in JS, it's equivalent to searching the whole string, i.e. not specifying that parameter at all. See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/lastIndexOf
However, in this library, the bounds check in lastIndexOf' means that e.g. lastIndexOf' (Pattern "a") 3 "aa" comes out as Nothing. I'd suggest getting rid of this check entirely, so that this matches better with the JS behaviour. This is a breaking change unfortunately.
Incidentally there are one or two other breaking changes I'd like to do (#81, #78, and also renaming Data.String.CodePoints to Data.String and renaming Data.String to Data.String.CodeUnits) so maybe we could do all of these the next time we break everything (i.e. when we release 0.12?)
Can we do this as part of the updates for 0.14?
This is one of those sneaky hidden breaking changes that isn't communicated in the types, it's a shame there's not a good way of knowing how much code this is likely to affect 😕
I think this is such a weird behaviour that someone almost certainly would have opened an issue by now if they had actually run into it.