MediaWiki/docs/globals.txt

globals.txt

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,
which are documented in DefaultSettings.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.

For a description of the classes, see design.txt.

$wgTitle
	Title object created from the request URL.

$wgOut
	OutputPage object for HTTP response.

$wgUser
	User object for the user associated with the current request.

$wgLang
	Language object selected by user preferences.

$wgContLang
	Language object associated with the wiki being viewed.

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

$wgRequest
	WebRequest object, to get request data

$wgMemc, $messageMemc
	Object caches