docs/design.txt

   1 design.txt
   2
   3 This is a brief overview of the new design.
   4
   5 More thorough and up-to-date information is available on the documentation
   6 wiki at https://www.mediawiki.org/
   7
   8 Primary classes:
   9
  10   User
  11     Encapsulates the state of the user viewing/using the site. Can be queried
  12     for things like the user's settings, name, etc. Handles the details of
  13     getting and saving to the "user" table of the database, and dealing with
  14     sessions and cookies.
  15
  16   OutputPage
  17     Encapsulates the entire HTML page that will be sent in response to any
  18     server request. It is used by calling its functions to add text, headers,
  19     etc., in any order, and then calling output() to send it all. It could be
  20     easily changed to send incrementally if that becomes useful, but I prefer
  21     the flexibility. This should also do the output encoding. The system
  22     allocates a global one in $wgOut.
  23
  24   Title
  25     Represents the title of an article, and does all the work of translating
  26     among various forms such as plain text, URL, database key, etc. For
  27     convenience, and for historical reasons, it also represents a few features
  28     of articles that don't involve their text, such as access rights.
  29     See also title.txt.
  30
  31   Article
  32     Encapsulates access to the "page" table of the database. The object
  33     represents a an article, and maintains state such as text (in Wikitext
  34     format), flags, etc.
  35
  36   Revision
  37     Encapsulates individual page revision data and access to the
  38     revision/text/blobs storage system. Higher-level code should never touch
  39     text storage directly; this class mediates it.
  40
  41   Skin
  42     Encapsulates a "look and feel" for the wiki. All of the functions that
  43     render HTML, and make choices about how to render it, are here, and are
  44     called from various other places when needed (most notably,
  45     OutputPage::addWikiText()). The StandardSkin object is a complete
  46     implementation, and is meant to be subclassed with other skins that may
  47     override some of its functions. The User object contains a reference to a
  48     skin (according to that user's preference), and so rather than having a
  49     global skin object we just rely on the global User and get the skin with
  50     $wgUser->getSkin().
  51     See also skin.txt.
  52
  53   Language
  54     Represents the language used for incidental text, and also has some
  55     character encoding functions and other locale stuff. The current user
  56     interface language is instantiated as $wgLang, and the local content
  57     language as $wgContLang; be sure to use the *correct* language object
  58     depending upon the circumstances.
  59     See also language.txt.
  60
  61   Parser
  62     Class used to transform wikitext to html.
  63
  64   LinkCache
  65     Keeps information on existence of articles. See linkcache.txt.
  66
  67 Naming/coding conventions:
  68
  69   These are meant to be descriptive, not dictatorial; I won't presume to tell
  70   you how to program, I'm just describing the methods I chose to use for myself.
  71   If you do choose to follow these guidelines, it will probably be easier for
  72   you to collaborate with others on the project, but if you want to contribute
  73   without bothering, by all means do so (and don't be surprised if I reformat
  74   your code).
  75
  76   - I have the code indented with tabs to save file size and so that users can
  77     set their tab stops to any depth they like. I use 4-space tab stops, which
  78     work well. I also use K&R brace matching style. I know that's a religious
  79     issue for some, so if you want to use a style that puts opening braces on
  80     the next line, that's OK too, but please don't use a style where closing
  81     braces don't align with either the opening brace on its own line or the
  82     statement that opened the block--that's confusing as hell.
  83
  84   - Certain functions and class members are marked with /* private */, rather
  85     than being marked as such. This is a hold-over from PHP 4, which didn't
  86     support proper visibilities. You should not access things marked in this
  87     manner outside the class/inheritance line as this code is subjected to be
  88     updated in a manner that enforces this at some time in the near future, and
  89     things will break. New code should use the standard method of setting
  90     visibilities as normal.
  91
  92   - Globals are particularly evil in PHP; it sets a lot of them automatically
  93     from cookies, query strings, and such, leading to namespace conflicts; when
  94     a variable name is used in a function, it is silently declared as a new
  95     local masking the global, so you'll get weird error because you forgot the
  96     global declaration; lack of static class member variables means you have to
  97     use globals for them, etc. Evil, evil.
  98
  99     I think I've managed to pare down the number of globals we use to a scant
 100     few dozen or so, and I've prefixed them all with "wg" so you can spot errors
 101     better (odds are, if you see a "wg" variable being used in a function that
 102     doesn't declare it global, that's probably an error).
 103
 104     Other conventions: Top-level functions are wfFuncname(), names of session
 105     variables are wsName, cookies wcName, and form field values wpName ("p" for
 106     "POST").