Detailed explanation of automatic loading of PHP files

This time I will bring you PHP filesAutomatic loadingDetailed explanation of use, what are the Notes for automatic loading of PHP files, the following is a practical case, let's take a look.

Traditionally, in PHP, when we want to use a class file, we have to require or include it at the head of the document:

<?php
require_once('../includes/functions.php');
require_once('../includes/database.php');
require_once('../includes/user.php');
...

But once there are many documents to be called , you have to write one line each time, which doesn’t look pretty. Is there any way to make the PHP document load automatically?

<?php
function autoload($class_name)
{
  require "./{$class_name}.php";
}

Yes, you can use PHP’s magic function autoload(). The above example is to automatically load the PHP file in the current directory. Of course, in practice, we are more likely to use it like this:

<?php
function autoload($class_name)
{
  $name = strtolower($class_name);
  $path = "../includes/{$name}.php";
  
  if(file_exists($path)){
     require_once($path);
    }else{
      die("the file {$class_name} could not be found");
    }
}

That is to say, we do a certain case processing of the file name, and then check whether the file exists before require. If it does not exist, display customized information. .

Similar usage is often seen in private projects, or in the framework of a single project. Why? Because you can only define one autoload function, in multi-person development, it is impossible for different developers to use different customized autoloaders, unless everyone agrees in advance to use one autoload, and synchronize versions when changes are involved. , which is very troublesome.

Mainly because of this, the good news is that this autoload function will soon be deprecated in version 7.2 of PHP.

Warning This feature has been DEPRECATED as of PHP 7.2.0. Relying on this feature is highly discouraged.
Then it is replaced by something called spl_autoload_register(), which has the advantage of being customizable Multiple autoloaders.

//使用匿名函数来autoload
spl_autoload_register(function($class_name){
  require_once('...');
});

//使用一个全局函数
function Custom()
{
  require_once('...');
}
spl_autoload_register('Custom');

//使用一个class当中的static方法
class MyCustomAutoloader
{
  static public function myLoader($class_name)
  {
    require_once('...');    
  }
}
//传array进来，第一个是class名，第二个是方法名
spl_autoload_register(['MyCustomAutoloader','myLoader']);

//甚至也可以用在实例化的object上
class MyCustomAutoloader
{
  public function myLoader($class_name)
  {
  }
}
$object = new MyCustomAutoloader;
spl_autoload_register([$object,'myLoader']);

It is worth mentioning that using autoload, whether it is autoload() or spl_autoload_register(), compared with require or include, the advantage is that the autoload mechanism is lazy loading, that is, it does not It is not that all those files are called for you as soon as you run it, but only the ones you use, such as which files are new, will the corresponding files be loaded through the autoload mechanism.

Of course, spl_autoload_register is often used in laravel including various packages, such as here:

/**
 * Prepend the load method to the auto-loader stack.
 *
 * @return void
 */
protected function prependToLoaderStack()
{
  spl_autoload_register([$this, 'load'], true, true);
}

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related topics on the PHP Chinese website article!

Recommended reading:

Detailed explanation of the steps to implement dependency injection using PHP class reflection

How to delete files in the directory using PHP unlink and rmdir accomplish

The above is the detailed content of Detailed explanation of automatic loading of PHP files. For more information, please follow other related articles on the PHP Chinese website!