PHP 范围解析操作符（::）用法分析【访问静态成员和类常量】

<?php
class MyClass {
  const CONST_VALUE = 'A constant value';
}

$classname = 'MyClass';
echo $classname::CONST_VALUE; // 自 PHP 5.3.0 起

echo MyClass::CONST_VALUE;

<?php
class OtherClass extends MyClass
{
  public static $my_static = 'static var';

  public static function doubleColon() {
    echo parent::CONST_VALUE . "\n";
    echo self::$my_static . "\n";
  }
}

$classname = 'OtherClass';
echo $classname::doubleColon(); // 自 PHP 5.3.0 起

OtherClass::doubleColon();

<?php
class MyClass
{
  protected function myFunc() {
    echo "MyClass::myFunc()\n";
  }
}

class OtherClass extends MyClass
{
  // 覆盖了父类的定义
  public function myFunc()
  {
    // 但还是可以调用父类中被覆盖的方法
    parent::myFunc();
    echo "OtherClass::myFunc()\n";
  }
}

$class = new OtherClass();
$class->myFunc();