globals.txt
-PHP loves globals. I hate them. This is not a great
-combination, but I manage. I could get rid of most of
-them by having a single "HTTP request" object, and using
-it to hold everything that's now global (which is exactly
-what I'd do in a Java servlet). But that's really
-awkward in PHP, and wouldn't really provide much benefit
-in readability or maintainability, so I go with the flow
-of PHP and use globals. Here's documentation on the
-important globals used by the system.
+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.
$wgLang
- Language object for this request.
+ Language object selected by user preferences
+
+$wgContLang
+ Language object associated with the wiki being
+ viewed.
$wgArticle
- Article object corresponsing to $wgTitle.
+ Article object corresponding to $wgTitle.
$wgLinkCache
LinkCache object.
-...
+$wgParser
+ Parser object. Parser extensions register their
+ hooks here.
+$wgLoadBalancer
+ A LoadBalancer object, manages database connections.