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How to implement singleton without using static/global variable? Possible?
One of the reason for most people saying that Singleton is evil is that it provides a global point of access or it becomes like a global variable. Is it possible to implement a singleton without having any kind of global variable including static. Is it possible to do this in C#.NET ?
The problem you are hinting at is that a Singleton becomes like a global var. What it uses is irrelevant.
And the answer would be No. You will always need a static somewhere, you can only defer it. And that kind of defeats the point.
No, that wouldn't be a singleton then.
You can use an IoC container to only inject things as a singleton.
You could implement an interface and then use something like StructureMap. In SM you would build the class like this:
public class Foo : IFoo
{
}
And then you would define, in your container, the following:
ObjectFactory.Initialize(x =>
{
x.For<IFoo>.Singleton().Use<Foo>();
}
Then you would inject this resource where you needed it:
public class Bar
{
public Bar(IFoo foo)
{
}
}
So, now there will only ever be one instance of the concrete created and then injected into an enumerable number of types that need it.
I don't believe so. If there isn't a static variable, where do you store the instance? Normally when I want a singleton of a class, I make all the constructors private and provide a static method or property that will create the instance if it hasn't already been created, and return the instance. The instance itself is stored as a private variable, so the only way to access it is through the provided method/property -- or reflection.
