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This article mainly introduces the example analysis of the principle of automatic loading in composer, which has a certain reference value, and interested friends can refer to it. I hope you will gain a lot after reading this article.

An in-depth analysis of the preface of the automatic loading principle of composer

PHP has been reborn since version 5.3, and the advent of namespaces, trait, closures, interfaces, PSR specifications, and composer have turned PHP into a modern scripting language. The ecosystem of PHP has been evolving, and the emergence of composer has completely changed the way of building PHP applications in the past. We can mix and match the most appropriate PHP components according to the needs of PHP applications. Of course, this also benefits from the proposal of the PSR specification.

Outline

PHP automatic loading function

PSR specification

Automatic loading process of comoposer

Composer source code analysis

1. PHP automatic loading function the origin of PHP automatic loading function

During PHP development, if you want to introduce a Class from outside, you usually use the include and require methods to include the file that defines the Class. When this is developed on a small scale, there is no big problem. However, in large development projects, using this approach will bring some implicit problems: if a PHP file needs to use many other classes, then it will require a lot of require/include statements, which may cause omissions or include unnecessary class files. If a large number of files need to use other classes, it must be a nightmare to make sure that each file contains the correct class file, and the performance of require or incloud is costly.

PHP5 provides a solution to this problem, which is the autoload mechanism of classes. The autoload mechanism, also known as Lazy loading (lazy loading), makes it possible for PHP programs to automatically include class files when they are used, rather than include all class files in the first place.

To sum up, the autoload feature brings several advantages:

Include / require is not required before using classes

Include / require files are only used when classes are used, which implements lazy loading and avoids redundant include / require files.

There is no need to consider the actual disk address of the imported class, and the separation of logic and entity files is realized.

PHP automatically loads the function _ _ autoload ()

Starting with PHP5, when we use a class, if we find that the class is not loaded, we will automatically run the _ _ autoload () function, which is customized in the program, in which we can load the class we need to use. Here is a simple example:

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