An inherited singleton class from a base class that takes parameters in its constructor?

Question

public class BaseFoo
{
    private string param;

    public BaseFoo(string param)
    {
        this.param = param;
    }
}

public sealed class SingletonFoo : BaseFoo
{
    static readonly SingletonFoo instance = new SingletonFoo();

    static SingletonFoo()
    {
    }

    public static SingletonFoo Instance
    {
        get
        {
            return instance;
        }
    }
}

Is this kind of inheritance possible, where the base class requires a constructor with parameters? (The above code won't obviously compile because no parameter is passed to the base class.)

If yes, how is it accomplished?

Answer 1

You use the 'base' keyword:

public SingletonFoo (string param) : base(param)
{
}

Answer 2

I'm pretty sure a 'singleton' deriving from a non-singleton base class completely invalidates the entire concept of the pattern, which is often used inappropriately to start with.

Static constructors do not take parameters, so the only way to pass them to the base class would be via constructor-chaining but I'm pretty sure you can't invoke an instance constructor from a static constructor...

What exactly are you trying to do here?

Answer 3

You need to make an instance constructor, and then refer to it:

public sealed class SingletonFoo : BaseFoo
{
    static readonly SingletonFoo instance = new SingletonFoo("Some Value");

    static SingletonFoo()
    {
    }

    private SingletonFoo(string value) : base(value)
    {
    }
    // ...

This will let you declare the parameter in the inline constructor, and call it down the chain.