Re: Getting an unknown error

$ perl -MDevel::Peek \
   -e'$x="abc"; Dump($x); Dump($1); for $1 ($x) { Dump($1); }'
SV = PV(0xd0e9e0) at 0xd2b810
  REFCNT = 1
  FLAGS = (POK,IsCOW,pPOK)
  PV = 0xd33f20 "abc"\0
  CUR = 3
  LEN = 10
  COW_REFCNT = 1
SV = PVMG(0xd23870) at 0xd36138
  REFCNT = 1
  FLAGS = (GMG,SMG)
  IV = 0
  NV = 0
  PV = 0
  MAGIC = 0xd44e10
    MG_VIRTUAL = &PL_vtbl_sv
    MG_TYPE = PERL_MAGIC_sv(\0)
    MG_OBJ = 0xd36120
    MG_LEN = 1
SV = PV(0xd0e9e0) at 0xd2b810
  REFCNT = 2
  FLAGS = (POK,IsCOW,pPOK)
  PV = 0xd33f20 "abc"\0
  CUR = 3
  LEN = 10
  COW_REFCNT = 1
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Before the loop, the symbol $1 accesses the scalar at address 0xd36138.

Inside the loop, the symbol $1 accesses the scalar at address 0xd2b810, which is the same scalar accessed by $x.

The read-only property of $1 is a property of the scalar. At your own request, you are not accessing that scalar within the body of the loop.

The capture fetching property of $1 is a property of the scalar. At your own request, you are not accessing that scalar within the body of the loop.

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Re^2: Getting an unknown error by oiskuu (Hermit) on Apr 24, 2015 at 17:15 UTC
Arguably, the lack of a warning is a bug here (at the very least). Note that the dynamic scoping of `$1` appears to be a property of the scalar as well. Masking it over will break pretty much anything called from within that loop, but not only—signal handlers break too. `$SIG{ALRM} = sub { "Yes" =~ /.*/; print "$&\n"; }; for $& ("No!") { alarm (1); sleep 2; }`	[reply] [d/l] [select]
Re^3: Getting an unknown error by ikegami (Patriarch) on Apr 27, 2015 at 01:18 UTC
As far as I'm concerned, anything other than `for my $var (LIST)` and `for $_ (LIST)` should be avoided. But it's probably best if enforced by `perlcritic` rather than warnings. Honestly, it's rather obvious that `$1` is special. If you start mucking with special vars, you get what you deserve.	[reply] [d/l] [select]