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• Is this a correct implementation of singleton C++?

  - by Kamal

  class A{ static boost::shared_ptr<A> getInstance(){ if(pA==NULL){ pA = new A(); } return boost::shared_ptr(pA); } //destructor ~A(){ delete pA; pA=NULL; } private: A(){ //some initialization code } //private assigment and copy constructors A(A const& copy); …

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• General question about Ruby Eigenclass/Singleton

  - by Dex

  module MyModule def my_method; 'hello'; end end class MyClass class << self include MyModule end end MyClass.my_method # => "hello I'm unsure why "include MyModule" needs to be in the eigenclass in order to be called using just MyClass. Why can't I go: X = MyClass.new X.my_method How is this type of pattern useful if…

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• Cocoa Singleton conventions

  - by MikeyWard

  Cocoa is full of singletons. Is there a logical/conventional difference between when the Cocoa APIs use NSSingletonObject *so = [NSSingletonObject defaultSingleton]; versus NSSingletonObject *so = [NSSingletonObject sharedSingleton]; ? Not a huge thing, but I don't really see why sometimes one is used versus the other.

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• Alternative to singleton for unique resources

  - by user1320881

  I keep reading over and over again that one should avoid using singletons for various reasons. I'm wondering how to correctly handle a situation where a class represents a unique system resource. For example, a AudioOutput class using SDL. Since SDL_OpenAudio can only be open once at a time it makes no sense having more then one object of this type…

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• What does your Objective-C singleton look like?

  - by schwa

  Mine is merely (or a close variant thereof): static MyClass *gInstance = NULL; + (MyClass *)instance { @synchronized(self) { if (gInstance == NULL) gInstance = [[self alloc] init]; } return(gInstance); }

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• C#: System.Lazy&lt;T&gt; and the Singleton Design Pattern

  - by James Michael Hare

  So we've all coded a Singleton at one time or another.  It's a really simple pattern and can be a slightly more elegant alternative to global variables.  Make no mistake, Singletons can be abused and are often over-used -- but occasionally you find a Singleton is the most elegant solution. For those of you not familiar with a Singleton,…

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• Database Context and Singleton injection with IoC

  - by zaitsman

  All of the below relates to a ASP.NET c# app. I have a Singleton Settings MemoryCache that reads values from database on first access and caches these, then invalidates them using SQL Service Broker message and re-reads as required. For the purposes of standard controllers, i create my Db Context in a request scope. However, this obviously means…

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• Singleton & Multi-threading

  - by ronan

  Friends I have the following class that class Singleton { private: static Singleton *p_inst; Singleton(); public: static Singleton * instance() { if (!p_inst) { p_inst = new Singleton(); } return p_inst; } }; Please do elaborate on precautions taken while implementing Singleton in multi-threaded environment…

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• Is it possible to apply inheritance to a Singleton class?

  - by Bragaadeesh

  Hi, Today I faced one question in interview. Is it possible to apply inheritance concept on Singleton Classes. I said since the constructor is private, we cannot extend that Singleton class (can someone please validate this). Next thing he asked me is to apply inheritance on that Singleton class. So, I made the Singleton's constructor as…

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• Can I use an abstract class instead of a private __construct() when creating a singleton in PHP?

  - by Pheter

  When creating a Singleton in PHP, I ensure that it cannot be instantiated by doing the following: class Singleton { private function __construct() {} private function __clone() {} public static function getInstance() {} } However, I realised that defining a class as 'abstract' means that it cannot be instantiated. So is…

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• Are Multiple singleton instances possible in a shared DLL?

  - by baris_a

  I am going to develop a DLL, and suppose I have a singleton class in this DLL with some synchronization mechanism. And this DLL is used by other processes, namely EXEs. The question is: is this singleton created only once for all sharing processes or every process has its own singleton?

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• Constructor and Destructor of a singleton object called twice

  - by Bikram990

  I'm facing a problem in singleton object in c++. Here is the explanation: Problem info: I have a 4 shared libraries (say libA.so, libB.so, libC.so, libD.so) and 2 executable binary files each using one another shared library( say libE.so) which deals with files. The purpose of libE.so is to write data into a file and if the executable…

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• Alternatives to the Singleton Design Pattern

  The Singleton Design Pattern is one of the simplest and most widely known design patterns in use in software development. However, despite its simplicity, it is very easy to get wrong and the consequences of its use even when properly implemented can outweigh its benefits. It turns out there are other ways to achieve the goals of the…

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• Hide or Show singleton?

  - by Sinker

  Singleton is a common pattern implemented in both native libraries of .NET and Java. You will see it as such: C#: MyClass.Instance Java: MyClass.getInstance() The question is: when writing APIs, is it better to expose the singleton through a property or getter, or should I hide it as much as possible? Here are the alternatives…

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• Singleton Properties

  - by coffeeaddict

  Ok, if I create a singleton class and expose the singleton object through a public static property...I understand that. But my singleton class has other properties in it. Should those be static? Should those also be private? I just want to be able to access all properties of my singleton class by doing this: …

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• How to bind a control to a singleton in Cocoa?

  - by SphereCat1

  I have a singleton in my FTP app designed to store all of the types of servers that the app can handle, such as FTP or Amazon S3. These types are plugins which are located in the app bundle. Their path is located by applicationWillFinishLoading: and sent to the addServerType: method inside the singleton to be…

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• Do I still have to implement a singleton class by hand in .net, even when using .Net4.0?

  - by Hamish Grubijan

  Once the singleton pattern is understood, writing subsequent singleton classes in C# is a brainless exercise. I would hope that the framework would help you by providing an interface or a base class to do that. Here is how I envision it: public sealed class Schablone : ISingleton<Schablone> { //…

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• Is this a valid, lazy, thread-safe Singleton implementation for C#?

  - by Matthew

  I implemented a Singleton pattern like this: public sealed class MyClass { ... public static MyClass Instance { get { return SingletonHolder.instance; } } ... static class SingletonHolder { public static MyClass instance = new MyClass (); } } From Googling…

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• Is there any reason for an object pool to not be treated as a singleton?

  - by Chris Charabaruk

  I don't necessarily mean implemented using the singleton pattern, but rather, only having and using one instance of a pool. I don't like the idea of having just one pool (or one per pooled type). However, I can't really come up with any concrete situations where there's an advantage to multiple pools…

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• Singleton Objects, C#

  In this article I will explain you about Singleton Objects using C#.

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• Could a singleton type replace static methods and classes?

  - by MKO

  In C# Static methods has long served a purpose allowing us to call them without instantiating classes. Only in later year have we became more aware of the problems of using static methods and classes. They can’t use interfaces They can’t use inheritance They are hard to test because you can’t…

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• Achieving C# "readonly" behavior in C++

  - by Tommy Fisk

  Hi guys, this is my first question on stack overflow, so be gentle. Let me first explain the exact behavior I would like to see. If you are familiar with C# then you know that declaring a variable as "readonly" allows a programmer to assign some value to that variable exactly once. Further attempts…

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• using a Singleton to pass credentials in a multi-tenant application a code smell?

  - by Hans Gruber

  Currently working on a multi-tenant application that employs Shared DB/Shared Schema approach. IOW, we enforce tenant data segregation by defining a TenantID column on all tables. By convention, all SQL reads/writes must include a Where TenantID = '?' clause. Not an ideal solution, but hindsight…

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• C++ Singleton design pattern.

  - by Artem Barger

  Recently I've bumped into realization/implementation of Singleton design pattern for C++. It has looked in the following way (I have adopted it from real life example): // a lot of methods is omitted here class Singleton { public: static Singleton* getInstance( ); ~Singleton( ); …

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• super(type,subclass) in simple singleton implementation

  - by Tianchen Wu

  when I was implementing naive singleton in python, I came up with a problem with super key word. As usual the behavior of super is always tricky and buggy, hope someone can shed light on it. Thanks :) The problem is that: class Singleton(object): def __new__(cls,*args,**kw): if not…

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