Question

I am trying to accomplish the following scenario that the generic TestClassWrapper will be able to access static properties of classes it is made of (they will all derive from TestClass). Something like:

public class TestClass
{
    public static int x = 5;
}

public class TestClassWrapper<T> where T : TestClass
{
    public int test()
    {
        return T.x;
    }
}

Gives the error:

‘T’ is a ‘type parameter’, which is not valid in the given context.

Any suggestions?

Answer 1

You can’t, basically, at least not without reflection.

One option is to put a delegate in your constructor so that whoever creates an instance can specify how to get at it:

var wrapper = new TestClassWrapper<TestClass>(() => TestClass.x);

You could do it with reflection if necessary:

public class TestClassWrapper<T> where T : TestClass
{
    private static readonly FieldInfo field = typeof(T).GetField("x");

    public int test()
    {
        return (int) field.GetValue(null);
    }
}

(Add appropriate binding flags if necessary.)

This isn’t great, but at least you only need to look up the field once…