Restricting T to string and int?

Question

I have built myself a generic collection class which is defined like this.

public class StatisticItemHits{...}

This class can be

Answer 1

You cannot restrict it to string and int from the where clause. You can check it in the constructor, but that is probably not a good place to be checking. My approach would be to specialize the class and abstract the class creation into a (semi-)factory pattern:

class MyRestrictedGeneric<T>
{
    protected MyRestrictedGeneric() { }


    // Create the right class depending on type T
    public static MyRestrictedGeneric<T> Create<T>()
    {
        if (typeof(T) == typeof(string))
            return new StringImpl() as MyRestrictedGeneric<T>;

        if (typeof(T) == typeof(int))
            return new IntImpl() as MyRestrictedGeneric<T>;

        throw new InvalidOperationException("Type not supported");
    }


    // The specialized implementation are protected away
    protected class StringImpl : MyRestrictedGeneric<string> { }
    protected class IntImpl : MyRestrictedGeneric<int> { }
}

This way you can limit the class's usage to just string and int internally inside your class.