in reply to Re: symbol/glob hash explanation
in thread symbol/glob hash explanation

right, I understand those examples, but what about when $sym is *Symbol::GEN0 ?

Is that hash "hidden" because it's not a simple name?

  DB<2> x $s = Symbol::gensym
0  GLOB(0x96f82b8)
   -> *Symbol::GEN0
  DB<3> x ${*$s}{goo} = 'ber'
0  'ber'
*  DB<4> x \%{*$s}
0  HASH(0x96f82e8)
   'goo' => 'ber'
  DB<5> x *$s
0  *Symbol::GEN0
  DB<6> x $s
0  GLOB(0x96f82b8)
   -> *Symbol::GEN0
  DB<7> x $Symbol::GEN0{goo}
0  undef
*  DB<8> x \%Symbol::GEN0
0  HASH(0x97783c0)
     empty hash
*  DB<9> x \%{Symbol::GEN0}
0  HASH(0x97783c0)
     empty hash
*  DB<10> x \%{*Symbol::GEN0}
0  HASH(0x97783c0)
     empty hash
*  DB<11> x \%{"Symbol::GEN0"}
0  HASH(0x97783c0)
     empty hash

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I've tried various ways of using the reference address and haven't found anything either.

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Re^3: symbol/glob hash explanation
by BrowserUk (Patriarch) on May 03, 2011 at 04:43 UTC
    I've tried various ways of using the reference address

    All except the right one :)

    You already did x ${*$s}{goo} = 'ber' and x *$s -> *Symbol::GEN0

    So try:x ${*Symbol::GEN0}{goo}

    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.
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      I did try that and it does not work, at least not on my 5.10.1

        DB<2> $s = Symbol::gensym

  DB<3> x ${*$s}{goo} = 'ber'
0  'ber'
*  DB<4> x \%{*$s}{goo}
syntax error at (eval 8)[/usr/share/perl/5.10/perl5db.pl:638] line 2, 
+near "}{goo"
*  DB<5> x \%{*$s}
0  HASH(0x86285e8)
   'goo' => 'ber'
*  DB<6> x \%{*Symbol::GEN0}
0  HASH(0x87144e0)
     empty hash
*  DB<7> x ${*Symbol::GEN0}{goo}
0  undef
  DB<8> x $]
0  5.010001
  DB<9> x $s
0  GLOB(0x86285b8)
   -> *Symbol::GEN0

      [download]

      ...

      *  DB<8> x \%{*Symbol::GEN0}
0  HASH(0x8aab260)
     empty hash
*  DB<9> x \%{*{Symbol::GEN0}}
0  HASH(0x8aab260)
     empty hash
*  DB<10> x \%{*{*Symbol::GEN0}}
0  HASH(0x8aab260)
     empty hash
*  DB<11> x \%{'' . *$s}
0  HASH(0x8aab260)
     empty hash
*  DB<12> x \%{*$s}
0  HASH(0x8a5b5e8)
   'goo' => 'ber'
*  DB<13> use Scalar::Util qw(refaddr)

  DB<14> x \%{*refaddr($s)}
syntax error at (eval 20)[/usr/share/perl/5.10/perl5db.pl:638] line 2,
+ near "*refaddr("
*  DB<15> x \%{refaddr($s)}
0  HASH(0x8b6eea0)
     empty hash
*  DB<16> x \%{sprintf "%x", refaddr($s)}
0  HASH(0x8b73ef0)
     empty hash
*  DB<17> x \%{*{"$s"}}
0  HASH(0x8b73c10)
     empty hash

      [download]

      It does not show up when I dump \%:: (or \%Symbol or \%Symbol:: or \%Symbol::GEN0 or \%Symbol::GEN0:: either (excluded for brevity) at least not that i can see.

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        Looking into Symbol, that is apparently deliberate:

        my $genpkg = "Symbol::";
my $genseq = 0;

sub gensym () {
    my $name = "GEN" . $genseq++;

    ## Instantiate the glob and take a reference to it.
    my $ref = \*{$genpkg . $name}; 

    ## Delete the name, leaving a reference to an anonymous glob
    delete $$genpkg{$name};        

    ## return the ref
    $ref;
}

        [download]

        Thus, it effectively mirrors the behaviour [] and {} in that you have a reference to a structure that doesn't (no longer) appears in the pad (symbol table).

        The few times I've wanted an anonymous glob I've used:

        $r = do{ \local *FRED };;
print $r;;
GLOB(0x4055f70)

        [download]
        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]

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