Limit instances creation of a class?

Question

I am using C#. I have created a class which can be included in any c#.net project (desktop or web based), but I want that only 10 objects will be created in that application

Answer 1

You'll simply need to use the factory pattern with a counter of the number of instances created, after which the factory method will throw an exception/return null.

Example:

public class Foobar
{
    private static int numInstances = 0;

    public static Foobar CreateFoobar()
    {
        if (numInstances++ < 10)
        {
            return new Foobar();
        }

        return null;
    }

    protected Foobar()
    {
        ...
    }
}

The above method will work perfectly well for a single-instance application, but for a multi-instance application, you'll probably want to use a semaphore (an implementation exists in System.Threading), which is intended for precisely this sort of situation (limiting access to resources/objects). It gets around the problem of multiple instances of the class being requested almost simultaneously and the count checks failing.