Reported the addition of magic: rt://49437

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]

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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

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.