Best way to carry & modify a variable through various instances and functions?

Question

I'm looking for the "best practice" way to achieve a message / notification system. I'm using an OOP-based approach for the script and would like to do something along the lines of this:

if(!$something)
   $messages->add('Something doesn\'t exist!');

The add() method in the messages class looks somewhat like this:

class messages {
   public function add($new) {
      $messages = $THIS_IS_WHAT_IM_LOOKING_FOR; //array

      $messages[] = $new;
      $THIS_IS_WHAT_IM_LOOKING_FOR = $messages;
   }
}

In the end, there is a method in which reads out $messages and returns every message as nicely formatted HTML.

So the questions is - what type of variable should I be using for $THIS_IS_WHAT_IM_LOOKING_FOR?

• I don't want to make this use the database. Querying the db every time just for some messages that occur at runtime and disappear after 5 seconds just seems like overkill.
• Using global constants for this is apparently worst practice, since constants are not meant to be variables that change over time. I don't even know if it would work.
• I don't want to always pass in and return the existing $messages array through the method every time I want to add a new message.
• I even tried using a session var for this, but that is obviously not suited for this purpose at all (it will always be 1 pageload too late).

Any suggestions?

Thanks!

EDIT: Added after I caused some confusion with the above... The $messages array should be global: I need to be able to add to it through various different classes as well as at the top-level of the whole script.

The best comparison that comes to mind is to use a database to store all the messages that occur at runtime, and when it's output-time, query the database and output every message. The exception to this comparison is just that the lifetime of the $messages array is the page load (they accumulate during page load, and vanish right after).

So, for example, say I have 10 different actions running one after the other in the script. Each one of these actions make use of a different class. Each one of these classes should be able to post to $messages->add(). After all 10 actions have run, it's "output time", and the $messages array can contain up to 10 different messages which were added via all the different classes.

I hope this clarifies it a bit.

Answer 1

I think you need either a instance field.

Answer 2

I'm not exactly clear about what you want to do, but a good way would be to simply use a private variable:

class messages {
   private $messages = array();
   public function add($new) {
     $this->messages[] = $new;
   }
   public function output() {
     // Whatever; e.g. a foreach loop that echoes all the messages
   }
}