Perl v5.8.5で内部文字列をsubstrするとbugる

substr_bug.pl

#!perl
use strict;
use warnings;
use utf8;
use Devel::Peek;

my $str = '{"a":"b","c":"あ"}';

Dump $str;
print <<EOS;
=====================================
@{[ substr($str, 2, 1) ]}
=====================================
EOS

my $sub = substr($str, 2);

Dump $str;
print <<EOS;
=====================================
@{[ substr($str, 2, 1) ]}
=====================================
EOS

v5.8.5

% perl -v

This is perl, v5.8.5 built for x86_64-linux-thread-multi

Copyright 1987-2004, Larry Wall

Perl may be copied only under the terms of either the Artistic License or the
GNU General Public License, which may be found in the Perl 5 source kit.

Complete documentation for Perl, including FAQ lists, should be found on
this system using `man perl' or `perldoc perl'.  If you have access to the
Internet, point your browser at http://www.perl.com/, the Perl Home Page.


% perl ~/substr_bug.pl
SV = PV(0x506550) at 0x525080
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,POK,pPOK,UTF8)
  PV = 0x517f00 "{\"a\":\"b\",\"c\":\"\343\201\202\"}"\0 [UTF8 "{"a":"b","c":"\x{3042}"}"]
  CUR = 19
  LEN = 20
=====================================
a
=====================================
SV = PVMG(0x551130) at 0x525080
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,SMG,POK,pPOK,UTF8)
  IV = 0
  NV = 0
  PV = 0x517f00 "{\"a\":\"b\",\"c\":\"\343\201\202\"}"\0 [UTF8 "{"a":"b","c":"\x{3042}"}"]
  CUR = 19
  LEN = 20
  MAGIC = 0x557120
    MG_VIRTUAL = &PL_vtbl_utf8
    MG_TYPE = PERL_MAGIC_utf8(w)
    MG_LEN = 17
    MG_PTR = 0x51a1b0
       0: 2 -> 2
       1: 15 -> 17
=====================================
a":
=====================================

v5.8.8

% perl -v

This is perl, v5.8.8 built for i386-linux-thread-multi

Copyright 1987-2006, Larry Wall

Perl may be copied only under the terms of either the Artistic License or the
GNU General Public License, which may be found in the Perl 5 source kit.

Complete documentation for Perl, including FAQ lists, should be found on
this system using "man perl" or "perldoc perl".  If you have access to the
Internet, point your browser at http://www.perl.org/, the Perl Home Page.


% perl ~/substr_bug.pl
SV = PV(0x9e96b00) at 0x9e96750
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,POK,pPOK,UTF8)
  PV = 0x9eacde8 "{\"a\":\"b\",\"c\":\"\343\201\202\"}"\0 [UTF8 "{"a":"b","c":"\x{3042}"}"]
  CUR = 19
  LEN = 20
=====================================
a
=====================================
SV = PVMG(0x9eab938) at 0x9e96750
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,SMG,POK,pPOK,UTF8)
  IV = 0
  NV = 0
  PV = 0x9eacde8 "{\"a\":\"b\",\"c\":\"\343\201\202\"}"\0 [UTF8 "{"a":"b","c":"\x{3042}"}"]
  CUR = 19
  LEN = 20
  MAGIC = 0x9ef4d08
    MG_VIRTUAL = &PL_vtbl_utf8
    MG_TYPE = PERL_MAGIC_utf8(w)
    MG_LEN = 17
    MG_PTR = 0x9ed21d8
       0: 2 -> 2
       1: 15 -> 17
=====================================
a
=====================================