PHP中如何形成static::與new static()的靜態系結

PHP中static::與new static()之後期靜態系結

一、parent、self、$this、__CLASS__

class A {}
class B extends A{
parent::(public|protected)(靜態方法|靜態變數)  ===> parent永遠是A
self::(public|protected)(靜態方法|靜態變數)  ===> self永遠是B
$this->(public|protected)(非靜態方法|非靜態變數)  ===> $this永遠是B的是範例化物件
__CLASS__    ===> 永遠是B
} 
class C extends B{
parent::(public|protected)(靜態方法|靜態變數)  ===> parent永遠是B
self::(public|protected)(靜態方法|靜態變數)  ===> self永遠是C
$this->(public|protected)(非靜態方法|非靜態變數)  ===> $this永遠是C的是範例化物件
__CLASS__    ===> 永遠是C 
}

二、static::

static關鍵字可以實現以下功能：

1 呼叫類的靜態方法 有後期靜態系結效果；

2 呼叫類的靜態屬性 有後期靜態系結效果；

3 呼叫類的非靜態方法 沒有後期靜態系結效果；

4 注意：不可以呼叫非靜態屬性；

class A {
    private static function foo() {
        echo "A success!n";
    }
    public function test() {
         $this->foo();
    }
}
 
class B extends A {
}
 
class C extends A {
    private static function foo() {
    echo "C success!n";
    }
}
 
$b = new B();
$b->test();//A success!
$c = new C();
$c->test();//A success!

class A {
    private static function foo() {
        echo "A success!n";
    }
    public function test() {
        static::foo();
    }
}
 
class B extends A {
}
 
class C extends A {
    private static function foo() {
    echo "C success!n";
    }
}
 
$b = new B();
$b->test();//A success!
$c = new C();
$c->test();//A無法呼叫C裡的私有foo方法 
 
 
 
 
//將C的foo改成非private(public|protected)就可以解決
class A {
    private static function foo() {
        echo "A success!n";
    }
    public function test() {
        static::foo();
    }
}
 
class B extends A {
}
 
class C extends A {
    public static function foo() {
    echo "C success!n";
    }
}
 
$b = new B();
$b->test();//A success!
$c = new C();
$c->test();//C success!

class A {
 public static function foo() {
     static::who();
 }
 
 public static function who() {
     echo __CLASS__."n";
 }
}
 
class B extends A {
 public static function test() {
     A::foo();
     parent::foo();
     self::foo();
 }
 
 public static function who() {
     echo __CLASS__."n";
 }
}
class C extends B {
 public static function who() {
     echo __CLASS__."n";
 } 
}
 
C::test(); 
A =>A::foo()的結果
C =>parent::foo()能走到A的foo,裡面static::who找C::who
C =>self::foo()能走到B的foo,B繼承A,走到A的foo,裡面static::who找C::who
 
 
 
 
 
class A {
    protected static function foo() {
        static::who();
    }
 
    protected static function who() {
        echo __CLASS__."n";
    }
}
 
class B extends A {
    public static function test() {
        A::foo();
        parent::foo();
        self::foo();
    }
 
    protected static function who() {
        echo __CLASS__."n";
    }
}
class C extends B {
    protected static function who() {
        echo __CLASS__."n";
    } 
}
 
C::test(); //A C C,解釋同上
 
 
 
 
 
class A {
 public static function foo() {
     static::who();
 }
 
 private static function who() {
     echo __CLASS__."n";
 }
}
 
class B extends A {
 public static function test() {
     A::foo();
     parent::foo();
     // self::foo();  
 }
 
 private static function who() {
     echo __CLASS__."n";
 }
}
class C extends B {
 private static function who() {
     echo __CLASS__."n";
 } 
}
 
C::test();
//A =>A::foo()的結果 
//報錯 A不可C的私有方法who => parent::foo()能走到A的foo,裡面static::who找C::who,C的who只能在C裡呼叫，不能在A裡呼叫
//報錯 A不可C的私有方法who => self::foo()能走到B的foo,B繼承A,走到A的foo,裡面static::who找C::who,C的who只能在C裡呼叫，不能在A裡呼叫

三、new static()

//new self()與new static()的區別，官網例子如下： 
class A {
  public static function get_self() {
    return new self();
  }
 
  public static function get_static() {
    return new static();
  }
}
 
class B extends A {}
 
echo get_class(B::get_self()); // A
echo get_class(B::get_static()); // B
echo get_class(A::get_static()); // A

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