classmap

A classmap is a mapping from fully qualified class names to the file paths that contain their definitions. It is used by autoloaders to load class files on demand by performing a direct lookup, rather than relying on name-based directory traversal or namespace-to-directory rules.

In the PHP ecosystem, the classmap autoloading approach is commonly managed by Composer. In a project’s composer.json, the autoload section can specify a classmap, for example "autoload": { "classmap": [ "src/" ] }. When assets are generated or updated, Composer scans the listed paths and creates a file that maps class names to their exact file locations. The resulting autoloader can quickly locate and include a class by consulting this map.

Advantages of a classmap include fast, straightforward loading and compatibility with legacy code that does not follow PSR-4 or PSR-0 conventions. Disadvantages include the need to rebuild or refresh the map whenever new classes are added or removed, and the potential increase in memory usage due to storing many mappings. To improve performance, developers often run commands such as composer dump-autoload -o to generate an authoritative, optimized class map.

Example mappings might look like "App\\Utils\\Logger" => "/path/to/project/src/Utils/Logger.php". Classmaps are frequently used for performance-critical autoloading or as a supplement to other autoloading strategies within a project.

See also: Autoloading, Composer, PSR-4.