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====================
Constructor Parameters
====================

All `__construct()` methods in Solar have exactly one parameter: an
associative array. That array is then populated into the protected `$_config`
property used in all classes descended from the Solar [[base class]].

Most classes in the PHP world use a sequential set of parameters for
constructors; e.g., if you wanted to specify three pieces of information for a
constructor, you would do something like this:

{{code: php
    class Normal_Example {
        public $a = null;
        public $b = null;
        public $c = null;
        public function __construct($a, $b, $c)
        {
            $this->a = $a;
            $this->b = $b;
            $this->c = $c;
        }
    }

    $example = new Normal_Example('one', 'two', 'three')
}}

In comparison, Solar classes can be instantiated like this:

{{code: php
    class Solar_Example extends Solar_Base {
        // note that the config property is named for the class
        // with an underscore prefix.  this lets us collect the
        // parent config defaults as well.
        protected $_Solar_Example = array(
            'a' => null,
            'b' => null,
            'c' => null,
        );
    }

    $config = array(
        'a' => 'one',
        'b' => 'two',
        'c' => 'three'
    );
    
    $example = new Solar_Example($config);
}}

> **Note:** Usually Solar objects are instantiated via [[Solar::factory()]],
> not via direct instantiation as above, but you get the idea.

Why do things this way? The idea is to make it easy to read data from a
[[config file]] and automatically configure object instances.

In the Solar_Example class, the constructor parameter could easily be
read from a configuration file and passed to the Solar_Example
constructor, which is not so easy with the Normal_Example.
</markdown>