I expected the following to work: julia> a = [1,2,3,4,5] 5-element Array{Int64,1}: 1 2 3 4 5 julia> deleteat!(a, end-1:end) ERROR: syntax: unexpected "end" julia> a[end-1:end] 2-element Array{Int64,1}: 4 5 I expected it to delete the last two variables in the array, instead it errors out.…

In particular the parser (or rather the “lowering” phase that happens right after parsing) converts any end inside a[...] into a call to endof(a). You can see this explicitly by calling @code_lowered: julia> f(a) = a[end-1:end] f (generic function with 1 method) julia> @code_lowered f([1,2,3,4])…

Thanks everyone for the explanations. That makes sense. But is this the best behavior? Could the parser not just recognize ends that are parts of ranges and convert those to Base.endof?

[image] tlnagy: Could the parser not just recognize ends that are parts of ranges and convert those to Base.endof? I can’t really answer that question, but I think it’s more complicated. To expand on Steven’s reply, the lowering of end is context-sensitive. For example, within a multi-dimens…

I took this too far :smile:: https://github.com/JobJob/EndyIndexes.jl pkg> add https://github.com/JobJob/EndyIndexes.jl.git using EndyIndexes const start_ = StartBasedIdx() const end_ = EndBasedIdx() arr = [1:10;] for idx in (end_-2:end_, start_+1:end_-2) @show arr[idx] end a = [1,2,3,4,5] d…

Maybe this is a good point to make advertisement for the idea for 2.0 to use $begin and $end as they are nice and free, unsurprising, and the dollar works as metaphor (the parser is supposed to substitute them by something like endof(a) and $ indicates talking to the parser. )

Seems like EndpointRanges.jl also does this? [image] EndpointRanges.jl Julia package for doing arithmetic on endpoints in array indexing

As this thread has been resurrected, it seems that endof() was deprecated. We can use lastindex() instead.

I don’t know why we don’t use first and last for this… Could also be useful for Unicode string from-end indexing. Example: my_string[first+2:last-2] could efficiently form a substring omitting the first two and last two characters of a Unicode string.

You do know about begin and end? julia> str = "αβγ" "αβγ" julia> str[begin+2:end-2] "β" The usual caveats about indexing unicode apply.

[image] tim.holy: You do know about begin and end? Yes, but these only work for calculating indices within []; many times you might wish to calculate indices outside, such as in the OP. Hence, the motivation for EndyIndexes.jl , this suggestion for $begin and $end, and EndpointRanges.jl . (Not …

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

General Usage

lmtzx9h4qqnt March 22, 2023, 8:43pm 9

Seems like EndpointRanges.jl also does this?

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

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