Base Class

The Solar_Base class is a lightweight base class from which all other Solar classes descend (not including exceptions, which descend from the Solar_Exception class). This base class provides:

A standard __construct() method that reads from the config file, then combines the instantiation-time constructor parameters with the default config values for the class.
A $_config property to collect configuration values for the class and its parents.
An _exception() method for finding and returning exceptions with localized message text.
A locale() method for finding and returning localized text strings.
An apiVersion() method for finding the API version of the class.

Extending the Base Class

When you extend from the Solar_Base class, make sure the only constructor parameter is $config = null (this is how it receives instantiation-time configuration values) and that it calls the parent constructor at some point (with the $config parameter passed up the chain).

For example:

<?php
class Solar_Example extends Solar_Base {

    // default config values
    protected $_Solar_Example = array(
        'opt_1' => 'foo',
        'opt_2' => 'bar',
        'opt_3' => 'baz'
    );

    // constructor
    public function __construct($config = null)
    {
        // pre-parent setup code
        // ...

        // parent construction
        parent::__construct($config);

        // post-parent setup
        // ...
    }
}
?>

Config File Settings

Now, if your config file has an 'Solar_Example' group in it, those values will override any of the default values set by your class definition. Say your config file looks something like this:

<?php
$config = array();
// ...
$config['Solar_Example']['opt_3'] = 'dib';
// ...
return $config;
?>

When you instantiate the Solar_Example object, the config file values will override the default values, leaving all others in place:

<?php
$example = Solar::factory('Solar_Example');
/*
  The values of $example->_config are now:

  'opt_1' => 'foo'
  'opt_2' => 'bar'
  'opt_3' => 'dib' // from the config file
*/
?>

Instantiation Settings

Finally, if you specify a configuration array as the second parameter of Solar::factory(), those values override both the default values of the class definition and the Solar.config.php values.

<?php
$config = array('opt_2' => 'gir');
$example = Solar::factory('Solar_Example', $config);
/*
  The values of $example->_config are now:

  'opt_1' => 'foo' // as defined by the class
  'opt_2' => 'gir' // from the Solar::factory() instantiation config
  'opt_3' => 'dib' // from the config file
*/
?>

Order of Precedence

All of this is to say that the order of precedence for config values looks like this:

The values start as defined by the class,
And are overwritten by any config file values,
And are again overwritten by values set at instantiation time

Note that values not changed remain the same, so if you leave one out, it's not overwritten to be null.