They are called symbolic refs.

I must disagree with moritz. Using %:: instead of symbolic refs does not help at all. All the same problems and disadvantages exist because it does exactly the same thing. Using %:: has the additional disadvantage that it's not caught by use strict 'refs';. In fact, it's generally less readable and harder to code using %:: instead of symbolic refs, so it's usually a step backwards to use %::.

If you want to improve your approach, use accessors.

use strict;

{
  package Foo;
  my $str = 'foo str';
  sub str {
    my $class = shift;
    $str = $_[0] if @_;
    return $str;
  }
}

{
  package Bar;
  my $str = 'bar str';
  sub str {
    my $class = shift;
    $str = $_[0] if @_;
    return $str;
  }
}

my $class = 'Foo';
my $value = $class->str();
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