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.


$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.

$wgRequest
	WebRequest object, to get request data

$wgMemc, $messageMemc, $parserMemc
	Object caches

$wgMessageCache
	Message cache, to manage interface messages

