1 //传统模式 --这段代码能很好工作，但大量的重复代码很烦人,不想为每个DomainObject子类都创建这段相同代码吧？
 2 /*
 3
 4 abstract class DomainObject{}
 5
 6 class User extends DomainObject
 7 {
 8     public function __construct()
 9     {
10         echo __METHOD__;
11     }
12
13     public static function create()
14     {
15         return new self();
16     }
17
18 }
19 class Document extends DomainObject
20 {
21     public function __construct()
22     {
23         echo __METHOD__;
24     }
25
26     public static function create()
27     {
28         return new self();
29     }
30
31 }
32 User::create();
33 Document::create();
34 */
35
36 //能否这么干？ 实例化最初调用者,谁调用实例化谁。但是这里self是指向的抽象类DomainObject
37 //fatal error: Cannot instantiate abstract class DomainObject 无法实例化抽象方法
38 /*
39 abstract class DomainObject
40 {
41     public static function create()
42     {
43         return new self();
44     }
45 }
46
47 class User extends DomainObject{}
48 class Document extends DomainObject{}
49 User::create();
50 */
51
52 //5.3后 可以使用static关键字，延迟静态绑定，通俗的就是，static 指向的是最初调用者
53 abstract class DomainObject
54 {
55     public static function create()
56     {
57         return new static();
58     }
59 }
60 class User extends DomainObject
61 {
62     public function __construct()
63     {
64         echo __METHOD__;
65     }
66
67 }
68 class Document extends DomainObject
69 {
70 public function __construct()
71     {
72         echo __METHOD__;
73     }
74 }
75 User::create(); //User::__construct
76 Document::create();  //Document::__construct

 1 abstract class DomainObject
 2 {
 3     private $group;
 4     public function __construct()
 5     {
 6         //$this->group = self::getGroup();
 7         $this->group = static::getGroup();
 8     }
 9
10     public static function create()
11     {
12         return new static();
13     }
14
15     static function getGroup()
16     {
17         return 'default';
18     }
19 }
20
21 class User extends DomainObject{}
22 class Document extends DomainObject
23 {
24     static function getGroup()
25     {
26         return 'document';
27     }
28 }
29 class SpreadSheet extends Document{}
30
31 print_r(User::create());         //     [group:DomainObject:private] => default
32 print_r(Document::create());     //     [group:DomainObject:private] => document
33 print_r(SpreadSheet::create());  //     [group:DomainObject:private] => document