I was thinking that the defined test would exclude any bits of the slice I didn't want - with no side effects. But clearly reading the value to test it's defined-ness is enough to vivify.

You're testing too late. Besides betterworld's trick, or moritz's optimization, you could specifically test for defined-ness per element, rather than taking the slice first:

@b = map { defined($a[$_]) ? ($a[$_]) : () } (0..5);

In reply to Re: Avoiding vivification with array slice by jhourcle
in thread Avoiding vivification with array slice by jbert

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