PHP:从父类中的静态方法调用子构造函数

Question

我想在父类中有一个静态方法来创建我调用此方法的任何子类的实例。

一个更清楚的例子:

class parent {    public static method make_objects($conditions){        for (...){            // here i want to create an instance            // of whatever subclass i am calling make_objects on            // based on certain $conditions        }    }}class sub extends parent{    ...}$objects = sub::make_objects($some_conditions);

Answer 1

从 php 5.3 开始，您可以使用 static这个关键字

<?php
class A {
  public static function newInstance() {
    $rv = new static();  
    return $rv;
  }
}
class B extends A { }
class C extends B { }

$o = A::newInstance(); var_dump($o);
$o = B::newInstance(); var_dump($o);
$o = C::newInstance(); var_dump($o);

打印

object(A)#1 (0) {
}
object(B)#2 (0) {
}
object(C)#1 (0) {
}

编辑:另一个(类似的)例子

<?php
class A {
  public static function newInstance() {
    $rv = new static();  
    return $rv;
  }

  public function __construct() { echo " A::__construct\n"; }
}
class B extends A {
  public function __construct() { echo " B::__construct\n"; }
}
class C extends B {
  public function __construct() { echo " C::__construct\n"; }   
}

$types = array('A', 'B', 'C');
foreach( $types as $t ) {
  echo 't=', $t, "\n";
  $o = $t::newInstance();
  echo '  type of o=', get_class($o), "\n";
}

打印

t=A
 A::__construct
  type of o=A
t=B
 B::__construct
  type of o=B
t=C
 C::__construct
  type of o=C