For me this is the best way, make init private. Swift 3 \ 4 \ 5 syntax // MARK: – Singleton final class Singleton { // Can’t init is singleton private init() { } // MARK: Shared Instance static let shared = Singleton() // MARK: Local Variable var emptyStringArray = [String]() }
I’m not entirely sure what use case you are trying to satisfy. But it is possible to have a factory return instances of an object. You should be able to modify this to suit your needs. var ExampleApplication = angular.module(‘ExampleApplication’, []); ExampleApplication.factory(‘InstancedService’, function(){ function Instance(name, type){ this.name = name; this.type = type; } return { … Read more
Volatile is unnecessary. Well, sort of** volatile is used to create a memory barrier* between reads and writes on the variable. lock, when used, causes memory barriers to be created around the block inside the lock, in addition to limiting access to the block to one thread. Memory barriers make it so each thread reads … Read more
The real reason that borg is different comes down to subclassing. If you subclass a borg, the subclass’ objects have the same state as their parents classes objects, unless you explicitly override the shared state in that subclass. Each subclass of the singleton pattern has its own state and therefore will produce different objects. Also … Read more
Do it yourself during startup. var foo = new Foo(); services.AddSingleton<IFoo>(foo); Or “warm it up” public void Configure(IApplicationBuilder app) { app.ApplicationServices.GetService<IFoo>(); } or alternatively public void Configure(IApplicationBuilder app, IFoo foo) { … } But this feels just dirty and is more a problem with your design, if you do something that you shouldn’t in the … Read more
First, a little definition: a singleton method is a method that is defined only for a single object. Example: irb(main):001:0> class Foo; def method1; puts 1; end; end => nil irb(main):002:0> foo = Foo.new => #<Foo:0xb79fa724> irb(main):003:0> def foo.method2; puts 2; end => nil irb(main):004:0> foo.method1 1 => nil irb(main):005:0> foo.method2 2 => nil irb(main):006:0> … Read more
I don’t really see the need, as a module with functions (and not a class) would serve well as a singleton. All its variables would be bound to the module, which could not be instantiated repeatedly anyway. If you do wish to use a class, there is no way of creating private classes or private … Read more
You are looking for Enumerable.Empty<T>(). In other news the Java empty list sucks because the List interface exposes methods for adding elements to the list which throw exceptions.
You make sure one of the columns can only contain one value, and then make that the primary key (or apply a uniqueness constraint). CREATE TABLE T1( Lock char(1) not null, /* Other columns */, constraint PK_T1 PRIMARY KEY (Lock), constraint CK_T1_Locked CHECK (Lock=’X’) ) I have a number of these tables in various databases, … Read more
To understand the proper way to workaround Singletons, you need to understand what is wrong with Singletons (and global state in general): Singletons hide dependencies. Why is that important? Because If you hide the dependencies you tend to lose track of the amount of coupling. You might argue that void purchaseLaptop(String creditCardNumber, int price){ CreditCardProcessor.getInstance().debit(creditCardNumber, … Read more