As requested, here are a few analogies: The Earth The Universe The element oxygen (there are other elements, but only one oxygen. There are lots of oxygen molecules, but only one canonical oxygen element.) The concept of True The concept of False You could instantiate lots of True objects, but they will all refer to … Read more
I think an application configuration is an excellent use of the Singleton pattern. I tend to use it myself to prevent having to reread the configuration each time I want to access it and because I like to have the configuration be strongly typed (i.e, not have to convert non-string values each time). I usually … Read more
In C++11 it is thread safe: ยง6.7 [stmt.dcl] p4 If control enters the declaration concurrently while the variable is being initialized, the concurrent execution shall wait for completion of the initialization. In C++03: Under g++ it is thread safe. But this is because g++ explicitly adds code to guarantee it. One problem is that if … Read more
Kotlin “object” is thread-safe by construction. As you can see in any decompile/dumping tool, declared object is just final class with static instance initialization + language syntax sugar to simplify instance access
Castle Windsor uses the term “transient” to describe all non-Singleton objects. I personally prefer the term “non-Singleton” though.
You can achieve this using a combination of a self-referencing generic type constraint, and a “new()” type constraint. The “new” constraint ensures that any child class will always have a parameterless constructor, so _instance = new T(); will always work. The self-referencing type constraint ensures that the “Instance” static property always returns the correct Type; … Read more
Of course it causes an infinite loop ! You call the destructor, but the destructor also calls the destructor, so the destructor calls the destructor again… and again… If you want to use delete, you must use it from outside of the destructor and NOT call it again in the destructor. To do that, you … Read more
Make sure you read the discussion on this question/answer, too. Why should we separate alloc and init calls to avoid deadlocks in Objective-C? To expand on the race condition issue; the real fix is to not have indeterminate initialization within your application. Indeterminate or lazy initialization results in behavior that can easily change due to … Read more
The proxy generated for @Transactional behavior serves a different purpose than the scoped proxies. The @Transactional proxy is one that wraps the specific bean to add session management behavior. All method invocations will perform the transaction management before and after delegating to the actual bean. If you illustrate it, it would look like main -> … Read more
Static will not give you a singleton. Since there is no way of making a top-level class a singleton in Java, you have getInstance methods which will implement some logic to to be sure there is only one instance of a class. public class Singleton { private static Singleton singleton; private Singleton(){ } public static … Read more