A brief analysis of automatic loading of related files by classes in PHP

This article brings you relevant knowledge about PHP, which mainly introduces the relevant content of automatic class loading. Let's analyze the files related to automatic class loading in PHP. I hope it will be helpful to everyone.

Analysis of relevant files for automatic class loading in PHP

Automatic class loading

Composer is a PHP package Management tools that can be used to manage third-party libraries that applications depend on. Composer can load these dependencies through the autoloading feature.

Composer uses an autoloading mechanism that uses special PHP functions to load classes when needed. This function is called the autoloader function and is called before the PHP script starts executing.

When the PHP parser encounters an undefined class, it calls the autoloader function. The autoloader function accepts a class name as a parameter and uses this class name to determine which file should be loaded. For example, if the class name is Foo\\Bar, the autoloader function might try to load the /path/to/project/src/Foo/Bar.php file.

Composer itself has some built-in autoloading functions that can be used to load libraries that the application depends on. For example, Composer can load classes using the PSR-4 autoloading specification. This specification uses namespaces and file structures to determine which files should be loaded. To use PSR-4 automatic loading, you need to specify the namespace prefix and file path in the application's composer.json file

When using it, you usually only need to include the following class autoloading entry file to complete

require 'vendor/autoload.php';

PSR-4 class automatic loading specification

PSR-4 (PHP Standard Recommendation 4) is a type of PHP automatic loading specification. It provides a standard way to load PHP classes using namespaces and file structures.

In the PSR-4 specification, each namespace has a corresponding folder. For example, if you have a namespace Foo\\Bar, you can place the corresponding class files in the /path/to/project/src/Foo/Bar folder.

In the PSR-4 specification, the class name is usually the same as the file name. For example, if you have a namespace called Foo\\Bar and a class called Baz, you can place such definitions in the /path/to/project/src/Foo/Bar/Baz.php file.

When using the PSR-4 specification, you need to specify the namespace prefix and file path in your application's composer.json file. Composer uses this information to generate autoloading code and writes it into the autoload_psr4.php file. When your application runs, Composer loads this file and uses the autoloader function to load the class. [Recommended learning: PHP video tutorial]

Several file analysis

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##vendor/autoload.php

The entry file directly contains the autoload_real.php file, and calls the following method to register all available namespaces, classes, files, etc.

ComposerAutoloaderInitxxxxxx::getLoader()

vendor/composer/autoload_classmap.php

Returns an array containing all autoload files for a single class name→class file

vendor/composer/autoload_files.php

Returns an array containing all PHP files that need to be automatically loaded, usually some global functions, etc.

vendor/composer/autoload_namespaces.php

Returns an array containing the mapping relationship of automatically loaded namespaces.

vendor/composer/autoload_psr4.php

Returns an array containing a list of namespace → file paths that comply with the PSR-4 autoload specification.

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