Library¶
A library is a collection of reusable code, functions, classes, or constants, that provides specific functionality and can be included in different applications.
Libraries are included, and then executed: yet, they do not have an entry point of their own. The calling application controls when and how the library’s code is invoked. This distinguishes a library from a framework, which imposes a structure and calls the application’s code instead.
Libraries cover a wide range of concerns: string manipulation, date handling, HTTP clients, cryptography, image processing, data parsing, and more. Using a well-maintained library avoids reinventing the wheel and benefits from the work and review of the wider community.
In PHP, libraries are distributed through Composer and indexed on Packagist. A library is declared as a dependency in composer.json and loaded via the Composer autoloader. Choosing a library involves evaluating its activity, test coverage, license, and compatibility with the target PHP version.
Writing a library requires extra discipline compared to application code: the public API must be stable, backward compatibility must be maintained across versions, and the library should have no opinion about the application’s framework or infrastructure.
See also Packagist and Composer documentation.
Related : Composer, Packagist, Framework, Dependency, Class Autoloading, Open Source, Vendor Lock-in, Application Programming Interface (API), Dynamic Loading, Foreign Function Interface (FFI), Software Development Kit (SDK)
