Summary of php autoload automatic loading usage examples

When using classes in PHP, we must load them before use, whether through require or include, but there will be two problems that affect our decision to load

In PHP Autoload is provided to help us easily include files, but autoload is not able to handle all situations as imagined. Today we will record some of the problems with autoload that we encountered a few days ago.

Why use Autoload

When using a class in PHP, we must load it before use, whether it is through require or include method, but there will be two problems that affect our decision to load.

The first is that I don’t know where this class file is stored, and the other is that I don’t know when I need to use this file. Especially when there are a lot of project files, it is impossible to write a long string of require at the beginning of each file...

After PHP5, we can solve this problem through autoload. And after PHP5.1, spl_autoload_register() is also provided to provide a more complete loading mechanism.

After reading the article Autoloading in PHP, I understand the loading mechanism of Autoload. When a class is instantiated through new, PHP will load the corresponding file through the defined autoload function. If this class file If you use extends or implements and need to use other class files, PHP will re-run autoload to search and load the class files. If two requests for the same class file occur, an error will be reported. The author of the original article provided three interesting examples to illustrate this problem, which can be viewed by downloading the source code here.

Generally, there are many ways to solve the problem of finding files in the corresponding location when loading. The most commonly used one is to specify a specific naming standard.

Zend’s method

zend recommends one of the most popular methods, which is to include the path in the file name. For example, the following example:

// Main.class

function autoload($class_name) {
$path = str_replace('_', DIRECTORY_SEPARATOR, $ class_name);
require_once $path.'.php';
}

$temp = new Main_Super_Class(); All underscores will be replaced by separators in the path symbol, in the above example, we will go to the Main/Super/Class.php file

The disadvantage of this method is that during the encoding process, we must clearly know where the code file should be, and because

The file path is hard-coded in the class name. If we need to modify the folder structure, we must manually modify all class names.

'Include All' method

If you are in a development environment and don't care much about speed, it is very useful to use this method. convenient. By placing all class files in one or several specific folders, and then traversing to find and load them.

For example:

The code is as follows:

<?php 
  $arr = array ( 
    &#39;Project/Classes&#39;, 
    &#39;Project/Classes/Children&#39;, 
    &#39;Project/Interfaces&#39; 
  );
  foreach($arr as $dir) { 
    $dir_list = opendir($dir);
    while ($file = readdir($dir_list)) { 
      $path = $dir.DIRECTORY_SEPARATOR.$file; 
      if(in_array($file, array(&#39;.&#39;, &#39;..&#39;)) || is_dir($path)) 
        continue;
      if (strpos($file, ".class.php")) 
        require_once $path; 
    } 
  } 
?>

##Associated files and locations

Another method is to establish an association between the class file and its location

Configuration file, for example:

The code is as follows:

// configuration.php 
array_of_associations = array( 
  'MainSuperClass' = 'C:/Main/Super/Class.php', 
  'MainPoorClass' = 'C:/blablabla/gy.php' 
);

is called File

The code is as follows:

<?php 
  require &#39;autoload_generated.php&#39;;
  function autoload($className) { 
    global $autoload_list; 
    require_once $autoload_list[$className]; 
  }
  $x = new A(); 
?>

Of course, if there are too many files, it will be a troublesome thing to maintain, but which one is better than hardcoding the position in the class name? Okay?

Of course we don’t want to maintain this list manually, so we can use automatic generation of this file to achieve this. The corresponding file can be php\xml\json, etc. The author of the original article implemented such a tool. If you think about it carefully, this is not difficult to implement. The author of the original article even developed a small Autoload framework, which is worth learning.

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