Perl Module Basics

The STORE() method is almost as simple:

# method called when scalar is written to

sub STORE {

   my ($self, $val) = @_;

   # return if the vent is already in the requested state

   return $val if $val == $self >{vent_state};

   # open or close vent

   if ($val) {

     open_vent($self >{compartment});

   } else {

     close_vent($self >{compartment});

   }

   # store and return current vent state

   return $self >{vent_state} = $val;

}

STORE() receives two arguments, the object and the new value. The code checks to 

see if it can return right away if the vent is already in the requested position. It 

then calls the class methods close_vent() or open_vent() as necessary. Finally, it 

returns the set value. STORE() methods should return their new value so that chained 

assignment works as expected:

$foo = $thermo = 1;   # $foo == 1

It's possible to call object methods using a tied variable. There are two ways to 

get access to the underlying object. First, it's returned by tie(). Second, it can be 

retrieved from a tied variable using the tied() routine. For example, say you added 

a method to the BOA::Thermometer class called fan() to turn on and off a fan 

inside the vent. Client code could call this method as follows:

$thermo_obj = tie $thermo,  BOA::Thermometer , compartment => 10;

$thermo_obj >fan(1);  # turn on the fan

This will also work:

tie $thermo,  BOA::Thermometer , compartment => 10;

tied($thermo) >fan(1);  # turn on the fan

Using additional object methods, tied modules can provide enhanced functionality 

without giving up the simplicity of a tied variable interface.

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