C# generic casting exception

Question

I have run into an odd casting issue while using generics. The following code will throw an InvalidCastException even though clearly an int can be cast to a double. Can anyone explain this behaviour and how to bypass it?

public class TestClass<T>
{
    public T Cast(object o)
    {
        return (T)o;
    }
}

public void Main()
{
    TestClass<double> w = new TestClass<double>();
    double x = w.Cast(10);
}

Edit:

Since I am in .net 4.0 land anyway I have changed it to use 'dynamic' instead of 'object' and everything works as expected. Appreciate all the spot-on and quick replies.

Answer 1

But an object can't be cast to a double. The o parameter takes an object, not an int.

For example, the following code fails with an InvalidCastException:

 object o = 1000;
 double x = (double)o;

Answer 2

You can use TypeConverter to convert variables

        public class TestClass<T>
        {
            public T Cast(object o)
            {
                TypeConverter converter = TypeDescriptor.GetConverter(o);
                if (converter.CanConvertTo(typeof(T)))
                {
                   var result = converter.ConvertTo(o, typeof(T));
                   return (T)result;
                }

                throw new InvalidCastException(
                      string.Format("Cannot convert from {0} to {1}", o.GetType().Name, typeof(T).Name));
            }
        }