singleton | 易学教程

Service instantiated twice after APP_INITIALIZER

阅读更多关于 Service instantiated twice after APP_INITIALIZER

问题 Problem is: I need to make an http call and store an object that is needed for generate dynamic routes. So, I was taking advantage of the APP_INITIALIZER. // app.module.ts import { ApplicationService } from './application.service'; providers: [ ApplicationService, { provide: APP_INITIALIZER, useFactory: appServiceFactory, deps: [Injector, ApplicationService], multi: true }, ], function appServiceFactory(injector: Injector, appService: ApplicationService): Function { return () => { return

Service instantiated twice after APP_INITIALIZER

阅读更多关于 Service instantiated twice after APP_INITIALIZER

C++ templated class implementation of the multiton pattern

阅读更多关于 C++ templated class implementation of the multiton pattern

问题 I implemented the multiton pattern using a templated class in C++. #ifndef MULTITON_H #define MULTITON_H #include <map> template <typename Key, typename T> class Multiton { public: static void destroy() { for (typename std::map<Key, T*>::iterator it = instances.begin(); it != instances.end(); ++it) { delete (*it).second; } } static T& getRef(const Key& key) { typename std::map<Key, T*>::iterator it = instances.find(key); if (it != instances.end()) { return *(T*)(it->second); } T* instance =

PHP singleton database connection pattern

阅读更多关于 PHP singleton database connection pattern

问题 I've been working on a small project using PHP and MySQL. I've read a lot around about best practices on managing a connection and so on. I've also implemented (following some posts found around) a singleton class to manage MySQL connections. require_once 'config.inc.php'; class DbConn { private static $instance; private $dbConn; private function __construct() {} /** * * @return DbConn */ private static function getInstance(){ if (self::$instance == null){ $className = __CLASS__; self::

python Singleton 模式

阅读更多关于 python Singleton 模式

Singleton 模式，中文既为单实例模式。一、代码示例看一下普通的类： class Normal(object): _instance = [] config = '' def set(self,value): self.config = value def get(self): return self.confg if __name__ == '__main__': s1 = Normal () s1.set('s1') s2 = Normal() s2.set('s2') print id(s1) print id(s2) print s1.get() print s2.get() 运行结果： ubuntu@yee:/tmp$ python t.py 139782948272976 139782948273040 s1 s2 可以看到，代码中生成了两个实例，每个实例都拥有自己的内存空间。接下来看单实例的代码示例： class Singleton(object): _instance = [] config = '' def __new__(cls,*args,**kwargs): if not cls._instance: cls._instance = super(Singleton,cls).__new__(cls,*args,**kwargs)

Why enum singleton is lazy?

阅读更多关于 Why enum singleton is lazy?

问题 I saw answers like these, tried to clarify via comments, and was unsatisfied by examples here. Maybe it's time for this specific question... Why enum singleton implementation is called lazy ? public enum EnumLazySingleton { INSTANCE; EnumLazySingleton() { System.out.println("constructing: " + this); } public static void touchClass() {} } How it is different from eager implementation? public class BasicEagerSingleton { private static final BasicEagerSingleton instance = new BasicEagerSingleton