Hello monks,

In my learning curve, i touched symbol table for the second time. I read Of Symbol Tables and Globs and at the end i was sure to have understood. Now i'm reading Mastering Perl and precisely a chapter dedicated to Symbol table and typeglobs (chapter 8). There is an example that left me full of doubts; here i propose you a semplified version:

#!/usr/bin/perl

package Foo {
  $n = 10;
  show_foo( "After assignment" );

  delete $Foo::{'n'};

  show_foo( "After delete" );
  sub show_foo
  {
    print "-" x 10, $_[0], "-" x 10, "\n";
    print "\$n is $n\n";
    foreach my $name ( keys %Foo:: )
    {
      print "$name\n";
    }
  }
}#end of package Foo

##OUT
----------After assignment----------
$n is 10
show_foo
n
----------After delete----------
$n is 10
show_foo
[download]

The main question is: why this $n is still here with his well round value? The entry in the symbol table is gone the variable itself no!
The output of the example is correct but not explained by the book and (as ysth noticed see page 130 seems i'm not the only one to be confused).

When i asked this into the chat, the kind monk ysth pointed me to the first clearly stated sentence about the matter: an answer from ysth on another site.

That answer contains others choking examples about the matter:

  $n = 123;
  delete $::{n};
  eval '$n=456';
  print $n;
  eval 'print $n';

#OUT
123456
[download]

and

  $n = 123;
  sub get_n { $n }
  BEGIN { delete $::{n} }
  $n = 456;
  print get_n();
  print $n;

#OUT
123456
[download]

So there is a way to safely access and modify (so delete too) a specified entry in the symbol table or a specified slot in it (using the so called *foo{THING} notation). There is a gently way? or I need to nuke the package at whole? as in:

#!/usr/bin/perl

use Symbol qw(delete_package);

package Foo {
  $n = 10;
  show_foo( "After assignment" );

  sub show_foo
  {
    print "-" x 10, $_[0], "-" x 10, "\n";
    print "\$n is $n\n";
    foreach my $name ( keys %Foo:: )
    {
      print "$name\n";
    }
  }
}#end of package Foo

delete_package('Foo');

# package Foo again
package Foo{
 show_foo( "After delete" );
}

#OUT
----------After assignment----------
$n is 10
show_foo
n
Undefined subroutine & called at ...
[download]

The Symbol of the core module have intimidating BUGS section about the delete_package call.

Thanks for the attention.

L*