{"id":94,"date":"2017-05-03T16:25:39","date_gmt":"2017-05-03T14:25:39","guid":{"rendered":"http:\/\/blog.lab3216.com\/?p=94"},"modified":"2018-11-06T13:09:31","modified_gmt":"2018-11-06T12:09:31","slug":"les-singletons-design-pattern","status":"publish","type":"post","link":"https:\/\/blog.scribter.com\/?p=94","title":{"rendered":"Les singletons : design pattern"},"content":{"rendered":"

Un singleton est un design pattern dont l’objet consiste \u00e0 avoir\u00a0une classe qui ne peut \u00eatre instanci\u00e9e\u00a0qu’une seule fois.<\/p>\n

Ce serait\u00a0le cas typique de la configuration d’un site web. Il serait\u00a0absurde de cr\u00e9er plusieurs objets configuration s’agissant d’un seul et m\u00eame site web.<\/p>\n

A chaque instanciation de Config, on ferait par exemple:<\/p>\n

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$config1<\/span> = new Config(<\/span>)<\/span>;
\n
\n...
\n
\n$config2<\/span> = new Config(<\/span>)<\/span>;<\/div><\/td><\/tr><\/tbody><\/table><\/div>\n

Un nouvel objet Config est cr\u00e9\u00e9 \u00e0 chaque fois. Ce qui nous arrange pas vraiment.<\/p>\n

Une solution \u00e0 ce probl\u00e8me serait de de cr\u00e9er une\u00a0classe statique. Celle-ci n’ayant pas besoin d’\u00eatre instanci\u00e9e. Il s’av\u00e8re cependant que ces classe statiques ne peuvent pas disposer de constructeur, de plus g\u00e9rer l’h\u00e9ritage des classes statiques est assez complexe. (voir\u00a0Late Static Bindings<\/a>).<\/p>\n

La solution consiste donc \u00e0 cr\u00e9er une nouvelle instance de la classe seulement si aucune\u00a0instance de cette classe n’a d\u00e9j\u00e0 \u00e9t\u00e9\u00a0cr\u00e9\u00e9e.<\/p>\n

Supposons que notre classe Config soit charg\u00e9e de g\u00e9rer\u00a0la configuration de notre application qui se trouve dans un fichier config\/config.php.<\/p>\n

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<\/div><\/td>
<?php<\/span>
\n
\nclass<\/span> Config {<\/span>
\n  private<\/span> $settings<\/span> =<\/span> [<\/span>]<\/span>;<\/span>
\n  private<\/span> static $_instance<\/span>;<\/span>
\n
\n  public<\/span> static function<\/span> getInstance(<\/span>)<\/span>{<\/span>
\n    if<\/span>(<\/span>is_null<\/span><\/a>(<\/span>self<\/span>::<\/span>$_instance<\/span>)<\/span>)<\/span>{<\/span>
\n      self<\/span>::<\/span>$_instance<\/span> =<\/span> new<\/span> Config(<\/span>)<\/span>;<\/span>
\n    }<\/span>
\n    return<\/span> self<\/span>::<\/span>$_instance<\/span>;<\/span>
\n  }<\/span>
\n
\n  public<\/span> function<\/span> __construct(<\/span>)<\/span>{<\/span>
\n    $this<\/span>-><\/span>settings<\/span> =<\/span> require<\/span> dirnam(<\/span>__DIR__)<\/span> .<\/span> 'config\/config.php'<\/span>;<\/span>
\n  }<\/span>
\n}<\/span><\/div><\/td><\/tr><\/tbody><\/table><\/div>\n

C’est donc dans la m\u00e9thode :<\/p>\n

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public<\/span> static function<\/span> getInstance(<\/span>)<\/span>{<\/span>
\n    if<\/span>(<\/span>is_null<\/span><\/a>(<\/span>self<\/span>::<\/span>$_instance<\/span>)<\/span>)<\/span>{<\/span>
\n      self<\/span>::<\/span>$_instance<\/span> =<\/span> new<\/span> Config(<\/span>)<\/span>;<\/span>
\n    }<\/span>
\n    return<\/span> self<\/span>::<\/span>$_instance<\/span>;<\/span>
\n  }<\/span><\/div><\/td><\/tr><\/tbody><\/table><\/div>\n

que l’instance de Config est cr\u00e9\u00e9e. On voit bien ici, que\u00a0Config n’est instanci\u00e9\u00a0que s’il\u00a0n’existe pas encore\u00a0d’objet.<\/p>\n

A chaque endroit o\u00f9 j’ai besoin de ma configuration, je l’appelle de cette mani\u00e8re<\/p>\n

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<\/div><\/td>
$<\/span>config = Config::getInstance(<\/span>)<\/span>;<\/div><\/td><\/tr><\/tbody><\/table><\/div>\n

De cette fa\u00e7on, l’objet Config n’est cr\u00e9\u00e9 que s’il n’a pas d\u00e9j\u00e0 \u00e9t\u00e9 pr\u00e9alablement instanci\u00e9 .<\/p>\n","protected":false},"excerpt":{"rendered":"

Un singleton est un design pattern dont l’objet consiste \u00e0 avoir\u00a0une classe qui ne peut \u00eatre instanci\u00e9e\u00a0qu’une seule fois. Ce serait\u00a0le cas typique de la configuration d’un site web. Il serait\u00a0absurde de cr\u00e9er plusieurs objets configuration s’agissant d’un seul et m\u00eame site web. A chaque instanciation de Config, on ferait par exemple: 12345$config1 = new … Continuer la lecture de Les singletons : design pattern<\/span> →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"ub_ctt_via":"","footnotes":""},"categories":[9,6],"tags":[],"class_list":["post-94","post","type-post","status-publish","format-standard","hentry","category-design-patterns","category-development-web"],"featured_image_src":null,"author_info":{"display_name":"metouisa","author_link":"https:\/\/blog.scribter.com\/?author=1"},"_links":{"self":[{"href":"https:\/\/blog.scribter.com\/index.php?rest_route=\/wp\/v2\/posts\/94","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.scribter.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.scribter.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.scribter.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.scribter.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=94"}],"version-history":[{"count":12,"href":"https:\/\/blog.scribter.com\/index.php?rest_route=\/wp\/v2\/posts\/94\/revisions"}],"predecessor-version":[{"id":100,"href":"https:\/\/blog.scribter.com\/index.php?rest_route=\/wp\/v2\/posts\/94\/revisions\/100"}],"wp:attachment":[{"href":"https:\/\/blog.scribter.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=94"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.scribter.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=94"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.scribter.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=94"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}