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:

# Generate the article HTML as if viewed by a web request $article = new Article( Title::newFromText( $t ) ); $article->view;

versus # Save current globals $oldTitle = $wgTitle; $oldArticle = $wgArticle;

# Generate the HTML $wgTitle = Title::newFromText( $t ); $wgArticle = new Article; $wgArticle->view;

# Restore globals $wgTitle = $oldTitle $wgArticle = $oldArticle 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.

$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.

$wgParser Parser object. Parser extensions register their hooks here.

$wgLoadBalancer A LoadBalancer object, manages database connections.