doc: add quick intro to autoloading
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@ -15,3 +15,195 @@ The mapping is defined by files in `include/autoloader/` folder.
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Currently, only HTMLPurifier library is loaded using autoloader.
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## A quick introdution to class autoloading
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The autoloader it's a way for php to automagically include the file that define a class when the class is first used, without the need to use "require_once" every time.
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Once is setup you don't have to use it in any way. You need a class? you use the class.
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At his basic is a function passed to the "spl_autoload_register()" function, which receive as argument the class name the script want and is it job to include the correct php file where that class is defined.
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The best source for documentation is [php site](http://php.net/manual/en/language.oop5.autoload.php).
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One example, based on fictional friendica code.
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Let's say you have a php file in "include/" that define a very useful class:
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```
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file: include/ItemsManager.php
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<?php
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namespace \Friendica;
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class ItemsManager {
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public function getAll() { ... }
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public function getByID($id) { ... }
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}
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```
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The class "ItemsManager" has been declared in "Friendica" namespace.
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Namespaces are useful to keep things separated and avoid names clash (could be that a library you want to use defines a class named "ItemsManager", but as long as is in another namespace, you don't have any problem)
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If we were using composer, we had configured it with path where to find the classes of "Friendica" namespace, and then the composer script will generate the autoloader machinery for us.
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As we don't use composer, we need check that the autoloader knows the Friendica namespace.
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So in "include/autoloader/autoload_psr4.php" there should be something like
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```
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$vendorDir = dirname(dirname(dirname(__FILE__)))."/library";
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$baseDir = dirname($vendorDir);
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return array(
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"Friendica" => array($baseDir."/include");
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);
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```
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That tells the autoloader code to look for files that defines classes in "Friendica" namespace under "include/" folder. (And btw, that's why the file has the same name as the class it defines.)
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*note*: The structure of files in "include/autoloader/" has been copied from the code generated by composer, to ease the work of enable autoloader for external libraries under "library/"
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Let's say now that you need to load some items in a view, maybe in a fictional "mod/network.php".
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Somewere at the start of the scripts, the autoloader was initialized. In Friendica is done at the top of "boot.php", with "require_once('include/autoloader.php');".
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The code will be something like:
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```
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file: mod/network.php
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<?php
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function network_content(&$a) {
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$itemsmanager = new \Friendica\ItemsManager();
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$items = $itemsmanager->getAll();
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// pass $items to template
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// return result
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}
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```
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That's a quite simple example, but look: no "require()"!
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You need to use a class, you use the class and you don't need to do anything more.
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Going further: now we have a bunch of "*Manager" classes that cause some code duplication, let's define a BaseManager class, where to move all code in common between all managers:
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```
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file: include/BaseManager.php
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<?php
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namespace \Friendica;
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class BaseManager {
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public function thatFunctionEveryManagerUses() { ... }
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}
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```
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and then let's change the ItemsManager class to use this code
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```
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file: include/ItemsManager.php
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<?php
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namespace \Friendica;
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class ItemsManager extends BaseManager {
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public function getAll() { ... }
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public function getByID($id) { ... }
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}
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```
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The autoloader don't mind what you need the class for. You need a class, you get the class.
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It works with the "BaseManager" example here, it works when we need to call static methods on a class:
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```
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file: include/dfrn.php
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<?php
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namespace \Friendica;
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class dfrn {
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public static function mail($item, $owner) { ... }
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}
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```
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```
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file: mod/mail.php
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<?php
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mail_post($a){
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...
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\Friendica\dfrn::mail($item, $owner);
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...
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}
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```
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If your code is in same namespace as the class you need, you don't need to prepend it:
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```
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file: include/delivery.php
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<?php
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namespace \Friendica;
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// this is the same content of current include/delivery.php,
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// but has been declared to be in "Friendica" namespace
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[...]
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switch($contact['network']) {
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case NETWORK_DFRN:
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if ($mail) {
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$item['body'] = ...
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$atom = dfrn::mail($item, $owner);
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} elseif ($fsuggest) {
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$atom = dfrn::fsuggest($item, $owner);
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q("DELETE FROM `fsuggest` WHERE `id` = %d LIMIT 1", intval($item['id']));
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} elseif ($relocate)
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$atom = dfrn::relocate($owner, $uid);
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[...]
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```
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This is real "include/delivery.php" unchanged, but as the code is declared to be in "Friendica" namespace, you don't need to write it when you need to use the "dfrn" class.
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But if you want to use classes from another library, you need to use the full namespace, e.g.
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```
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<?php
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namespace \Frienidca;
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class Diaspora {
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public function md2bbcode() {
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$html = \Michelf\MarkdownExtra::defaultTransform($text);
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}
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}
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```
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if you use that class in many places of the code and you don't want to write the full path to the class everytime, you can use the "use" php keyword
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```
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<?php
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namespace \Frienidca;
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use \Michelf\MarkdownExtra;
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class Diaspora {
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public function md2bbcode() {
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$html = MarkdownExtra::defaultTransform($text);
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}
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}
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```
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Note that namespaces are like paths in filesystem, separated by "\", with the first "\" being the global scope.
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You can go more deep if you want to, like:
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```
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<?php
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namespace \Friendica\Network;
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class DFRN {
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}
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```
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or
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```
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<?php
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namespace \Friendica\DBA;
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class MySQL {
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}
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```
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So you can think of namespaces as folders in a unix filesystem, with global scope as the root ("\").
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