Question

I am using silverlight 4.0 in my application. I have a method in my base class as mentioned below

class BaseClass
{
    protected CustomRequest GetCustomRequest(IEnumerable<IRequestType> types)
    {
        //Some code here...
    }
}

In my derived class when I call this method like below I get error

IEnumerable<RequestType> requestTypes = CodeToGetThis();
GetCustomRequest(requestTypes)

Note here that in calling statement the type of requestTypes is a enumerable of derived type of IRequestType.

This works well in desktop applications due to introduction of covariance in c#4.0. But it seems that for silverlight 4.0 it is not done for IEnumerable interface.

So what is the best alternative approach I should use in my silverlight application for this?

I somewhere read that it can be done using method overloading but not sure how to do this.

UPDATE:
One thing I missed in the first draft of the question is, I will have many derived types of IRequestType hence craeating overloaded method for each derived type will be a difficulty for me.

Answer 1

Just cast each item to the interface e.g.

IEnumerable<IRequestType> requestTypes = CodeToGetThis().Select(x => (IRequestType)x);
GetCustomRequest(requestTypes)

You could do something with method overloading and have a method that took your derived/concrete type but you would only end up doing something like the above and calling the original method in the overload.