plugin.php

/**
 * Four Ways to Hook into WordPress when using a Class 
 *
 * Do NOT place the action hook in the `_construct`.
 *
 * @link https://carlalexander.ca/designing-class-wordpress-hooks/
 */

/**
 * Call init from outside the class.
 *
 * But need to pass values to the construct.
 */
class MyPlugin_1
{
    public function init()
    {
        add_action('wp_loaded', array($this, 'on_loaded'));
    }
 
    public function on_loaded()
    {
        // ...
    }
}
$my_plugin_1 = new MyPlugin_1();
$my_plugin_1->init();

/**
 * Place the action hook outside of the class (decouple).  Version I.
 * 
 * This requires *two* actions to get it going.
 */
class MyPlugin_2
{
    public static function init()
    {
        $self = new self();
        add_action('wp_loaded', array($self, 'on_loaded'));
    }
 
    public function on_loaded()
    {
        // ...
    }
}
add_action('plugins_loaded', array('MyPlugin_2', 'init'));

/**
 * Call a class from a static method as a custom constructor.
 *
 * This method is the briefest, when calling. Requires only one action hook.
 *
 * Not sure if can pass a value to the construct here if the method is static.
 */
class MyPlugin_3
{
    public static function init()
    {
        $self = new self();
        add_action('wp_loaded', array($self, 'on_loaded'));
    }
 
    public function on_loaded()
    {
        // ...
    }
}
MyPlugin_3::init();

/**
 * Place the action hook outside of the class (decouple). Version II.
 * 
 * No action hook is *inside* the class. This should result in the greatest portability.
 */
class MyPlugin_4
{
    public function on_loaded()
    {
        // ...
    }
}
 
$my_plugin = new MyPlugin_4();
add_action('wp_loaded', array($my_plugin, 'on_loaded'));

/*
 * Conclusion: The last two may be the "best". 
 *
 * #3 is the briefest to call.
 * #4 places all action hooks outside of WordPress. May be the best if logic only is needed,
 * but no direct interaction with WordPress.
 */