in reply to Re^4: perl5.10 Devel::Size behaviour changed? (bug report)
in thread perl5.10 Devel::Size behaviour changed?

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.

Replies are listed 'Best First'.
Re^6: perl5.10 Devel::Size behaviour changed? (bug report)
by BrowserUk (Patriarch) on Sep 04, 2009 at 19:29 UTC

    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.
[reply]
[d/l]
[select]

      D::S also uses AvARRAY, AvALLOC and AvARYLEN. 

      use strict;
use warnings;

use Devel::Peek qw( Dump );

use Inline C => <<'__EOI__';
void call_AvMAX(AV* av)    { AvMAX(av);    }
void call_AvARRAY(AV* av)  { AvARRAY(av);  }
void call_AvALLOC(AV* av)  { AvALLOC(av);  }
void call_AvARYLEN(AV* av) { AvARYLEN(av); }
__EOI__

my @a = qw( a b c );  print("After init:\n");        Dump(\@a, 1);
call_AvMAX(\@a);      print("\nAfter AvMAX:\n");     Dump(\@a, 1);
call_AvARRAY(\@a);    print("\nAfter AvARRAY:\n");   Dump(\@a, 1);
call_AvALLOC(\@a);    print("\nAfter AvALLOC:\n");   Dump(\@a, 1);
call_AvARYLEN(\@a);   print("\nAfter AvARYLEN:\n");  Dump(\@a, 1);

      [download]
      After init:
SV = RV(0x238c18) at 0x238c0c
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x182a68c
  SV = PVAV(0x2399f4) at 0x182a68c
    REFCNT = 2
    FLAGS = (PADMY)
    ARRAY = 0x1824504
    FILL = 2
    MAX = 3
    ARYLEN = 0x0
    FLAGS = (REAL)

After AvMAX:
SV = RV(0x238c18) at 0x238c0c
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x182a68c
  SV = PVAV(0x2399f4) at 0x182a68c
    REFCNT = 2
    FLAGS = (PADMY)
    ARRAY = 0x1824504
    FILL = 2
    MAX = 3
    ARYLEN = 0x0
    FLAGS = (REAL)

After AvARRAY:
SV = RV(0x238c18) at 0x238c0c
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x182a68c
  SV = PVAV(0x2399f4) at 0x182a68c
    REFCNT = 2
    FLAGS = (PADMY)
    ARRAY = 0x1824504
    FILL = 2
    MAX = 3
    ARYLEN = 0x0
    FLAGS = (REAL)

After AvALLOC:
SV = RV(0x238c18) at 0x238c0c
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x182a68c
  SV = PVAV(0x2399f4) at 0x182a68c
    REFCNT = 2
    FLAGS = (PADMY)
    ARRAY = 0x1824504
    FILL = 2
    MAX = 3
    ARYLEN = 0x0
    FLAGS = (REAL)

After AvARYLEN:
SV = RV(0x238c18) at 0x238c0c
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x182a68c
  SV = PVAV(0x2399f4) at 0x182a68c
    REFCNT = 2
    FLAGS = (PADMY,RMG)
    MAGIC = 0x23fdbc
      MG_VIRTUAL = &PL_vtbl_arylen_p
      MG_TYPE = PERL_MAGIC_arylen_p(@)
      MG_FLAGS = 0x02
        REFCOUNTED
    ARRAY = 0x1824504
    FILL = 2
    MAX = 3
    ARYLEN = 0x0
    FLAGS = (REAL)

      [download]

      So AvARYLEN is the culprit. In 5.10.1, AvARYLEN is defined as 

      #define AvARYLEN(av)    (*Perl_av_arylen_p(aTHX_ MUTABLE_AV(av)))

      [download]

      Sounds familiar.

[reply]
[d/l]
[select]

In Section Seekers of Perl Wisdom