php类自动装载和php链式操作的原理

<?php
namespace Tests;
class Test1{
  static function test(){
    echo __CLASS__.'<br>';
    echo __FILE__.'<br>';
  }
}

<?php
include "load.php";
TestsTest1::test();

<?php
class Loader
{
  static function loadClass($class)
  {
    $class =  __DIR__.DIRECTORY_SEPARATOR.str_replace('\','/',$class).'.php';
    if (file_exists($class)) {
      include $class;
      return;
    }
  }
}
spl_autoload_register(array('Loader','loadClass'));

<?php
 
class db
{
    public function where()
    {
    //code here
    }
    public function order()
    {
    //code here
    }
    public function limit()
    {
    //code here
    }
}

<?php
 
$db = new db();
 
$db->where();
$db->order();
$db->limit();

<?php
 
class db
{
    public function where()
    {
    //code here
    return $this;
    }
    public function order()
    {
    //code here
    return $this;
    }
    public function limit()
    {
    //code here
    return $this;
    }
}

<?php
 
$db = new db();
 
$db->where()->order()->limit();