If it's a bug, it's not attributable to Devel::Size. Any operation that queries the size does the same thing:

perl -MDevel::Peek -e "my @a; Dump \@a, 1; printf qq[SIZE :%d\n], $#a;
+ Dump \@a, 1"
SV = RV(0x34e158) at 0x34e148
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x276630
  SV = PVAV(0x34efb8) at 0x276630
    REFCNT = 2
    FLAGS = (PADMY)
    ARRAY = 0x0
    FILL = -1
    MAX = -1
    ARYLEN = 0x0
    FLAGS = (REAL)
SIZE :-1
SV = RV(0x34e290) at 0x34e280
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x276630
  SV = PVAV(0x34efb8) at 0x276630
    REFCNT = 2
    FLAGS = (PADMY,RMG)
    MAGIC = 0x27fde8
      MG_VIRTUAL = &PL_vtbl_arylen_p
      MG_TYPE = PERL_MAGIC_arylen_p(@)
      MG_FLAGS = 0x02
        REFCOUNTED
      MG_OBJ = 0x34e148
      SV = PVMG(0x261f18) at 0x34e148
        REFCNT = 1
        FLAGS = (GMG,SMG,pIOK)
        IV = -1
        NV = 0
        PV = 0
        MAGIC = 0x27fcf8
          MG_VIRTUAL = &PL_vtbl_arylen
          MG_TYPE = PERL_MAGIC_arylen(#)
          MG_OBJ = 0x276630
    ARRAY = 0x0
    FILL = -1
    MAX = -1
    ARYLEN = 0x34e148
    FLAGS = (REAL)
[download]

The reason a change was made:

From Nicholas Clark reply-to Eric Brine, perl5 porters <perl5-porters@perl.org> to Eric Brine cc perl5 porters <perl5-porters@perl.org> date Fri, Sep 4, 2009 at 2:55 PM subject Re: 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

Hm. Pre-5.10, every array that didn't use $#array, wasted 1 pointer.

Post 5.10, every array uses that pointer to point to a 12 or 24-byte block of memory whether it is ever used or not.

And the very act of attempting to check to see if there is any magic attached, causes there to be magic attached.

That makes no sense at all to me.

Now the only way D::S can avoid causing the magic to be attached is to either not bother looking to see if there is any; or to dereference the magic pointer directly...

A microscopic optimisation attempt that causes a macroscopic [sic] pessimisation. Autovivifying magic just because someone wants to know if there is any is...

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

RIP PCW It is as I've been saying!(Audio until 20090817)

Any operation that queries the size does the same thing:

Not so.

>perl -MDevel::Peek -le"my @a = qw(a b c); print @a-1; Dump \@a,1"
2
SV = RV(0x238c60) at 0x238c54
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x182a22c
  SV = PVAV(0x239a4c) at 0x182a22c
    REFCNT = 2
    FLAGS = (PADMY)
    ARRAY = 0x182521c
    FILL = 2
    MAX = 3
    ARYLEN = 0x0
    FLAGS = (REAL)
[download]

If it's a bug, it's not attributable to Devel::Size.

If it's a bug that reading $#a adds magic to @a, then that's not attributable to D::S.

The bug in D::S is that it should be using the method that doesn't add magic.

I see you removed the "rvalue" reference...

Anyway, the code of D::S does this:

   if (AvMAX(thing) != -1) {
      /* an array with 10 slots has AvMax() set to 9 - te 2007-04-22 *
+/
      total_size += sizeof(SV *) * (AvMAX(thing) + 1);
[download]

And AvMAX is defined as:

#define AvMAX(av)    ((XPVAV*)  SvANY(av))->xav_max
[download]

Ie. It simply gets the value from a struct member.

It also references AvALLOC & AvARYLEN, but neither of those does anything with magic either:

#define AvARRAY(av)    ((av)->sv_u.svu_array)
#define AvALLOC(av)    (*((SV***)&((XPVAV*)  SvANY(av))->xav_alloc))
#define AvMAX(av)    ((XPVAV*)  SvANY(av))->xav_max
#define AvFILLp(av)    ((XPVAV*)  SvANY(av))->xav_fill
#define AvARYLEN(av)    (*Perl_av_arylen_p(aTHX_ MUTABLE_AV(av)))
[download]

The only "method" that touches magic is AvFILL:

#define AvFILL(av)    ((SvRMAGICAL((const SV *) (av))) \
             ? mg_size(MUTABLE_SV(av)) : AvFILLp(av))
[download]

And AvFILL doesn't appear anywhere in the D::S source.

So, I say again, the bug does not lie with D::S.

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

RIP PCW It is as I've been saying!(Audio until 20090817)