C# Lawyer: How to Create an Instance of a Generic Type with Parameters

Following code doesn't compile:

    class GenericFactory where T : new()
    {
        public T Create(object a, object b)
        {
            return new T(a, b);
        }
    }

The compiler will give you following error message: "'T': cannot provide arguments when creating an instance of a variable type.". Well, there are a couple ways to solve this issue.

Use reflection

    class GenericFactory
    {
        public T Create(object a, object b)
        {

            return (T) typeof(T).GetConstructor(new System.Type[] { typeof(object), typeof(object) }).Invoke(new object[] {a, b});
        }
    }

Use intialization

Following code uses an initialization interface to solve this issue. You can also use properties instead of a method.

    interface I
    {
        void Initialize(object a, object b);
    }

    class GenericFactory where T : I, new()
    {
        public T Create(object a, object b)
        {
            T t = new T();
            t.Initialize(a, b);
            return t;
        }
    }

There are a few other ways available. I will update this article later.

See also

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