Simple usage of Perl state variables

I see this type of code too often:

package Foo;
{
  my $structure = {};
  sub plop {
      #...
      $structure->{$foo} = 'bar';
      #...
  }
}

Or things like that:

package Foo;
{
  my $cache;
  sub plop {
      #...
      defined $cache or $cache = _load_cache();
      #...
  }
}

If you are using a non-ancient version of Perl (that is, 5.10 or more), you should consider using the state keyword. It’s similar to the static variables inherited from C.

From the documentation :

state declares a lexically scoped variable, just like my does. However, those variables will never be reinitialized, contrary to lexical variables that are reinitialized each time their enclosing block is entered.

So the two code snippets become :

package Foo;
sub plop {
    state $structure = {};
    $structure->{$foo} = 'bar';
    #...
}

and:

package Foo;
sub plop {
    #...
    state $cache = _load_cache();
    #...
}

Nothing terribly amazing here, but it’s really easy, saves keystrokes and makes the code more readable. So why not use it more widely ?

Simple usage of Perl state variables

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