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I have an array reference that I would like to slice the last two elements of the array. I found that using -2..-1 would work. I was using the following syntax:

subroutine($var->[-2..-1]);

This gave me the following error:

Use of uninitialized value $. in range (or flip)
Argument "" isn't numeric in array element

I changed the line to this and that worked:

subroutine(@$var[-2..-1]);

I don't understand why the second way works though and the first doesn't. I thought using the array operator was the same as dereferencing with @. Is the context ambiguous with the arrow operator?

Warpstar22
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1 Answers1

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-> is the dereference operator. $aref->[$i] is to an $aref like $arr[$i] is to @arr. To get a slice from an array, you need to change the sigil: @arr[$i, $j]. It's similar for dereference, but instead of changing the sigil, you first dereference the reference, then slice it:

@{ $aref }[$i, $j]

which can be shortened to @$aref[$i, $j].

So the -> operator can only be used for single values for array and hash references. You need @{} for slices.

choroba
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    Additionally -- that error is popping up because Perl thinks you want a scalar in-between `[` and `]` (and not a list) in your subscript, so it assumes `..` is the flip-flop operator instead of the range operator. See [Range Operators](https://perldoc.pl/perlop#Range-Operators) para.3, "In scalar context..." – Jim Davis May 24 '22 at 15:13
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    Or `$aref->@[$i, $j]`. See [Perl Dereferencing Syntax](https://stackoverflow.com/q/46507722/589924) – ikegami May 24 '22 at 15:17