Manual:Global object variables

Globals are evil. The original MediaWiki code relied on globals for processing context far too often. MediaWiki development since then has been a story of slowly moving context out of global variables and into objects. Storing processing context in object member variables allows those objects to be reused in a much more flexible way. Consider the elegance of:

versus

Some of the current MediaWiki developers have an idle fantasy that some day, globals will be eliminated from MediaWiki entirely, replaced by an application object which would be passed to constructors. Whether that would be an efficient, convenient solution remains to be seen, but  certainly PHP 5 makes such object-oriented programming models easier than they were in previous versions.

For the time being though, MediaWiki programmers will have to work in an environment with some global context. At the time of writing, 418 globals were initialised on startup by  MediaWiki. 304 of these were configuration settings, set in DefaultSettings.php (see also the documentation there) and LocalSettings.php. There is no comprehensive documentation for the remaining 114 globals,  however some of the most important ones are listed below. They are typically initialised either in index.php or in Setup.php.

Global variables

 * $wgOut - OutputPage object for HTTP response.
 * $wgUser - User object for the user associated with the current request.
 * $wgTitle - Title object created from the request URL.
 * $wgLang - Language object selected by user preferences
 * $wgContLang - Language object associated with the wiki being viewed.
 * $wgArticle - Article object corresponding to $wgTitle.
 * $wgMessageCache - Message cache to manage interface messages
 * $wgRequest - WebRequest object, to get request data
 * $wgParser - Parser object. Parser extensions register their hooks here.
 * $wgLoadBalancer - LoadBalancer object, manages database connections.
 * Note: This variable doesn't exist anymore in 1.13
 * $mediaWiki - MediaWiki object, the main base class for the MediaWiki software. Initializes the $wgTitle and $wgArticle objects, and executes the URL actions.