Duplicate code is one of the most pungent code smells. A rule that is often used is to re-structure code once it is duplicated in three or more places.
Common duplication problems, and corresponding solutions are:
| 1 | <?php  | 
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| 9 | class Services { | 
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| 10 | |||
| 11 | /**  | 
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| 12 | * Store the current instance  | 
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| 13 | *  | 
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| 14 | * @access private  | 
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| 15 | * @var object Services  | 
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| 16 | * @static  | 
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| 17 | */  | 
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| 18 | private static $instance;  | 
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| 19 | |||
| 20 | /**  | 
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| 21 | * The array of services  | 
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| 22 | *  | 
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| 23 | * Should be of the format array( __FILE__ => __CLASS__ );  | 
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| 24 | *  | 
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| 25 | * @access private  | 
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| 26 | * @var array  | 
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| 27 | * @static  | 
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| 28 | */  | 
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| 29 | private $services = array();  | 
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| 30 | |||
| 31 | /**  | 
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| 32 | * The current schedule object  | 
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| 33 | *  | 
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| 34 | * @access private  | 
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| 35 | * @var object Scheduled_Backup  | 
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| 36 | */  | 
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| 37 | private $schedule;  | 
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| 38 | |||
| 39 | /**  | 
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| 40 | * Get the current instance  | 
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| 41 | *  | 
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| 42 | * @static  | 
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| 43 | */  | 
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| 44 | 	public static function instance() { | 
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| 52 | |||
| 53 | /**  | 
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| 54 | * Get the array of registered services  | 
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| 55 | *  | 
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| 56 | * @param Scheduled_Backup $schedule  | 
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| 57 | * @return Service[]  | 
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| 58 | */  | 
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| 59 | 	public static function get_services( Scheduled_Backup $schedule = null ) { | 
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| 70 | |||
| 71 | 	public function get_available_services() { | 
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| 72 | return $this->get_services();  | 
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| 73 | }  | 
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| 74 | |||
| 75 | /**  | 
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| 76 | * Register a new service  | 
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| 77 | *  | 
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| 78 | * @param $filepath  | 
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| 79 | * @param $classname  | 
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| 80 | * @return bool|WP_Error  | 
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| 81 | */  | 
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| 82 | View Code Duplication | 	public static function register( $filepath, $classname ) { | 
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| 91 | |||
| 92 | /**  | 
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| 93 | * De-register an existing service  | 
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| 94 | * @param string $filepath  | 
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| 95 | * @return bool|WP_Error  | 
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| 96 | */  | 
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| 97 | View Code Duplication | 	public static function unregister( $filepath ) { | 
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| 107 | |||
| 108 | /**  | 
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| 109 | * Instantiate the individual service classes  | 
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| 110 | *  | 
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| 111 | * @param string $classname  | 
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| 112 | *  | 
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| 113 | * @return array An array of instantiated classes  | 
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| 114 | */  | 
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| 115 | View Code Duplication | 	private static function instantiate( $classname ) { | 
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| 129 | |||
| 130 | }  | 
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| 131 | 
This check marks private properties in classes that are never used. Those properties can be removed.