{"id":8981,"date":"2020-08-31T11:00:46","date_gmt":"2020-08-31T02:00:46","guid":{"rendered":"https:\/\/www.gigas-jp.com\/appnews\/?p=8981"},"modified":"2020-08-28T20:41:05","modified_gmt":"2020-08-28T11:41:05","slug":"singleton-design-pattern","status":"publish","type":"post","link":"https:\/\/www.gigas-jp.com\/appnews\/archives\/8981","title":{"rendered":"Singleton Design Pattern"},"content":{"rendered":"\n

Singleton is one of the creational design pattern that allows you to ensure that a class has only one instance, while providing a global access point to this instance.<\/p>\n\n\n\n

Make the single instance object class responsible for creation, initialization, access, and execution. Declare the instance as a member of private static data. Provides a public static member function that encapsulates all initialization code and provides access to the instance.<\/p>\n\n\n\n

The client calls the access function (using the class name and the scope resolution operator) whenever a reference to the single instance is required.<\/p>\n\n\n\n

The singleton should be considered only if the following three criteria are met:<\/p>\n\n\n\n

Single instance ownership cannot reasonably be assigned
Lazy initialization is desirable
Global access is not provided otherwise<\/p>\n\n\n\n

Lets take a look at code samples<\/p>\n\n\n\n

PHP code sample<\/p>\n\n\n\n

<?php\n\n\/**\n * Singleton class\n *\/\nclass LogSingleton {\n    \/**\n     * I kept this attribute and constructor as private so that other sub class can't instantiate\n     * it can also be protected if you want to allow sub classes to be instantiated\n     *\/\n    private static $intance = null;\n\n    private function __construct() {\n    }\n\n    \/**\n     * I will assign the singleton instance if $instance is null.\n     * otherwise will return directly.\n     *\/\n    public static function log() {\n      if (self::$intance == null) {\n         self::$intance = new LogSingleton();\n      }\n      return self::$intance;\n    }\n\n    \/\/can also declare other public functions below.\n    public function debugLog()\n    {\n      return \"debug log\";\n    }\n  }\n\n\/\/client code\n$client = LogSingleton::log(); \/\/ this is the singleton instance.\nvar_dump($client->debugLog());\n<\/code><\/pre>\n\n\n\n
C# sample code<\/p>\n\n\n\n
using System;\n\nnamespace HelloWorld\n{\n    class LogSingleton\n    {\n        \/**\n         * I kept this attributes as private so that other sub class can't instantiate\n         * it can also be protected if you want to allow sub classes to be instantiated\n         *\/\n        private static LogSingleton instance;\n\n        \/**\n         * for the first use for this class, s_lock will have a object.\n         * This will later use along with lock function to protect from multi thread base.\n         *\/\n        private static readonly object s_lock = new object();\n\n        public static LogSingleton log()\n        {\n            if (instance == null)\n            {\n                \/**\n                 * The client who has s_lock will proceed this condition.\n                 *\/\n                lock (s_lock)\n                {\n                    \/**\n                     * I will assign the singleton instance if instance is null.\n                     * otherwise will return directly.\n                     *\/\n                    if (instance == null)\n                    {\n                        instance = new LogSingleton();\n                    }\n                }\n            }\n            return instance;\n        }\n\n        \/\/can also declare other public functions below.\n        public string debugLog()\n        {\n            return \"debug log\";\n        }\n\n        \/\/client code\n        class Program\n        {\n            static void Main(string[] args)\n            {\n                var client = LogSingleton.log(); \/\/ this is the singleton instance.\n                Console.WriteLine(client.debugLog());\n\n            }\n        }\n    }\n\n}\n<\/code><\/pre>\n\n\n\n
By Yuuma<\/p>\n
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<\/g:plusone><\/div>\n            
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