Using end variable in ranges passed to functions other than getindex?

[uniment]

And just today, another thread asking about this. It’s funny how interest in topics tends to bunch temporally

@ParadaCarleton

But we might need something for indexing from the end.

As you saw last time, I had talked myself out of this when I realized it doesn’t save any boundschecks. But then I saw this thread:

Base.Chop API rationale

Base.chop chop(s::AbstractString; head::Integer = 0, tail::Integer = 1) Remove the first head and the last tail characters from s. The call chop(s) removes the last character from s. If it is requested to remove more characters than length(s) then an empty string is returned. I am curious about the reasoning for two choices: uses keyword arguments instead of positional defaults to tail=1 Especially the default tail=1 I really am puzzled by: what is this function for?

Unicode makes the string API rather awkward, necessitating strange functions like chop; if we could access relative to first and last ordinal indices, methods like this wouldn’t be needed. Dictionaries and I imagine some other data structures could also make use of such indexing; I begin to wonder about sparse arrays.

Maybe it even makes sense to have both xs[begin:end] indexing and xs[first:last] indexing, where the former is understood to range over positional indices eachindex(xs), whereas the latter ranges over ordinal indices 1:length(xs)? (similar to the contrast between xs[i] vs xs[n*th])

@ParadaCarleton

We could try using Python’s -1st for ordinal indices?

I entertained that thought momentarily, but I was turned off when I realized the inconsistency in having 1st:-1st work but (1:-1)st not work. I’m not sure why unitrange a:b clamps to a:a-1 for b much less than a; maybe that can be changed?