How to get around the fact C# doesn't allow void as a generic parameter?

I have the following generic classes, which handle requests that return different kinds of objects:

class Request<T> {
    /* ... */

    public T Result { get; protected set; }
    public abstract bool Execute();
    protected bool ExecuteCore(params /* ... */) { /* ... */ }
}

class ObjectRequest<T> : Request<T>
    where T : class, new() { /* ... */ }

class ListRequest<T> : R开发者_开发问答equest<List<T>>
    where T : class, new() { /* ... */ }

class CompoundRequest<T, U> : Request<T>
    where T : class, IHeader<U>, new()
    where U : class, new() { /* ... */ }

class CompoundRequest<T, U, V> : Request<T>
    where T : class, IHeader<U>, IHeader<V>, IHeader<W>, new()
    where U : class, new()
    where V : class, new() { /* ... */ }

class CompoundRequest<T, U, V, W> : Request<T>
    where T : class, IHeader<U>, IHeader<V>, new()
    where U : class, new()
    where V : class, new()
    where W : class, new() { /* ... */ }

interface IHeader<T> {
    List<T> Details { get; set; }
}

Now I would like to create a class that handles requests that return no objects. However, setting a generic parameter to null is not allowed:

class NoReturnRequest : Request<void> { /* ... */ } // illegal

How do I get around this?

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I'd recommend flipping your design pattern around; first you should build a non-generic Request class that doesn't return anything, and from it inherit generic Request<T>, Request<T1, T2>, Request<T1, T2, T3>, etc.. classes that do return values.

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This is a common problem as languages such as C# become more functionally-oriented.

The Rx team solved it by introducing Unit.

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Generics are used for a typed parameters. If the parameter does not have type, use interface or abstract from another class (which your Request will also inherit from)