The reason a change was made:

FromNicholas Clark
reply-toEric Brine,
perl5 porters <perl5-porters@perl.org>
toEric Brine
ccperl5 porters <perl5-porters@perl.org>
dateFri, Sep 4, 2009 at 2:55 PM
subjectRe: rvalue $#a adds magic

On Fri, Sep 04, 2009 at 02:46:26PM -0400, Eric Brine wrote:
> Before 5.10, $#a didn't add magic to @a

> Since 5.10.0, it does.

> Is that intentional?
> What's the purpose?

It's storing the value for $#a in the magic. Most arrays don't use $#a, which means that before 5.10 nearly every array consumes 1 pointers-worth of memory just to store NULL.

I did it in 2005: http://perl5.git.perl.org/perl.git/commitdiff/a3874608cd3b

In reply to Re^5: perl5.10 Devel::Size behaviour changed? (reason for magic) by ikegami
in thread perl5.10 Devel::Size behaviour changed? by sang1986

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