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C#: Force constructor signature using abstract class?

I've been searching for a while on this because I'm naturally forgetful and I thought it would be nice to build something (an abstract class, interface, etc.?) that would force me to implement certain bits of code in a class I was writing.
In particular, I would like to force a new class to always have a constructor that takes a single parameter typed as itself in order to make duplication of the object easier. I've seen articles/questions elsewhere that talk about this, but I'm not sure this particular question has been asked (at least that I can find) or I'm simply not understanding enough of the other articles/questions to realize it. My apologies in advance.
I'm not interested in having a constructor in an abstract class, interface, etc. actually do anything. I'm merely interested in defining the requirement for a constructor signature in a derived class.
My ideal class would look like this:
public class GoodClass
{
public GoodClass(GoodClass goodClass)
{
// copy components of goodClass to this instance
}
}
So, I first began researching interfaces and also started reading up on abstract classes. I was thinking something like the code below would work, but alas I get errors. Is what I'm trying to do even possible? Is there any other way I could accomplish my goal without putting a sticky note on my monitor? :)
abstract class SelfConstructor
{
abstract public SelfConstructor(SelfConstructor) { }
}
class NewClass : SelfConstructor
{
//Required by SelfConstructor:
public NewClass(NewClass newClass)
{
// copy components of newClass to this instance
}
}

You could write a ReSharper plugin that recognises this case and highlights the class if it doesn't have a "copy constructor". This would be a daemon stage that would process the file as it's being edited, and add highlights. You can look through the abstract syntax tree of the file, look for all instances of IConstructorDeclaration, and then get the constructor's parameters from the ParameterDeclarations property. You can check that there is a constructor that only has one parameter, and that parameter is the same type as the class it's declared in.
You can compare the types by getting the constructor's parameter's TypeUsage and trying to downcast to IUserTypeUsage. You can then use ScalarTypeName.Reference.Resolve() to get an instance of IDeclaredElement. Compare this against the class's IClassDeclaration.DeclaredElement to see if they're the same instance.

In C++, what you are talking about is a copy constructor, you actually get one by default!
C# doesn't have that concept (though of course you can define one); however, it is easier (and preferred) to simply implement ICloneable (MSDN), which requires you to implement the Clone method, that does the same thing.
Instead of:
object myObj = new CloneableObject(otherObj);
You write:
object myObj = otherObj.Clone();
The other thing you could do is force a constructor signature by not having a default:
public class BaseClass
{
//No abstract constructors!
public BaseClass(BaseClass copy)
{
}
}
Now when you derive, you have to use that overload in the constructor. Nothing will force the derived signature, but at least you have to explicitly use it:
public class DerivedClass : BaseClass
{
public DerivedClass() : base(this)
{
}
}
The above example clearly shows that it doesn't "force" you to have a copy constructor, but like a sticky note, would serve as a good reminder.
I would definitely go the interface route, as that is what is there for (and you can use an abstract implementation!).
Note that you can take advantage of Object.MemberwiseClone if you want a shallow copy for free. All objects get this, no interface required.

Ensuring a generic collection contains objects that derive from two base objects

I have an interesting problem that I keep circling around, but I never seem to quiet find a solution.
I tend to be a defensive programmer, so I try to write code that prevents problems from happening rather than reacting to problems once they've occurred. To that end, I have the following situation. Take the following code:
public class Base {}
public Interface IBase {}
public class Derived : Base, IBase {}
public class Derived2 : Base, IBase {}
...
public class DerivedN : Base, IBase {}
public class X : Base {}
public class Y : IBase {}
I need to pass a list of objects that derive from Base and implement IBase to a collection, and I need to make sure that only objects that have both are added to the list. Additionally, there can be an arbitrary number of classes that have both, so I cannot use the derived classes as constraints.
If I make the list of type Base, then I could add a Y object. If I make it of type IBase, then objects of type X can be added (neither of which are permitted).
I could, of course create my own generic collection class that has both types and has constraints for both. But, I don't want to have to do this for all possible collection types, and it's a lot of effort to duplicate all that functionality (even if you just forward the method calls to a contained class).
I could also create a BaseWithIBase class, which derives from both Base and IBase, and use that as my collection type, but I really don't want to force another abstraction if I don't have to.
I don't want this to be a runtime check, so walking the tree and throwing exceptions is not acceptable.
Can anyone suggest a better approach to this problem?
NOTE: Base and IBase are not related, just pointing out they are both base items of different types.
EDIT:
It seems that everyone wants to insist that "you don't need to do that" and that it's "not OOP". Nothing could be further from the truth. I was attempting to remove the specific from the question to prevent these kinds of questions and comments, so I will include my real situation.
The code is an implement of a Windows Service framework, based on the .NET Frameworks ServiceProcess.ServiceBase class. I am adding my own framework on top of this, that is intended to be heavily Dependency Injection based, and highly testable.
The collection must contain objects that derive from both ServiceBase and IService. IService is my framework extension that is used in my code, and for testing. It is basically just this:
public interface IService
{
void Start();
void Stop();
}
In addition, I have a number of other interfaces:
public interface IRestartableService
{
void Restart();
}
public interface IConfigurableService
{
void Configure();
}
etc.. etc.. and a service may look like this:
public class MyService : ServiceBase, IService, IConfigurableService {}
My code requires IService, Windows requires ServiceBase, thus both are needed because I work with IService, and windows works with ServiceBase. I only require IService, the other interfaces are optional.

You can create your own wrapper collection simply:
// TODO: Work out which collection interfaces you want to implement
public class BaseList
{
// Or use List<IBase>, if that's how you'll be using it more often.
private List<Base> list = new List<Base>();
public void Add<T>(T item) where T : Base, IBase
{
list.Add(item);
}
}
By using a generic method with both constraints, you can be sure that Add can only be called with an appropriate type argument.
You could have two methods to expose the data as IEnumerable<T> - one returning IEnumerable<IBase> (using Cast<T>) and one returning IEnumerable<Base>... that would let you use LINQ on either type, but not both at the same time of course.
I suspect you may find this awkward elsewhere, however - you may find yourself littering your code with generic methods which you wouldn't typically need. While there may well be a good reason for wanting both the class part and the interface part, it would be worth taking a step back and considering whether they're really both necessary. Is there something extra you could add to the interface so that you could do away with the class constraint, for example?

There is no good answer to your question because the design itself is not really fitting OOP as implemented in C#/.NET.
If you absolutely need a collection where each element statically provides two independent interfaces, either a wrapper collection or some wrapper class like Wrapper<TFirst, TSecond, T> : IBoth<TFirst, TSecond> would solve your problem.
Example:
public interface IBoth<TFirst, TSecond> {
TFirst AsFirst();
TSecond AsSecond();
}
public class Wrapper<T, TFirst, TSecond> : IBoth<TFirst, TSecond>
where T : TFirst, TSecond
{
private readonly T _value;
public Wrapper(T value) {
_value = value;
}
public TFirst AsFirst() {
return _value;
}
public TSecond AsSecond() {
return _value;
}
}
However the real question is why do you need that. Not to say that standard OOP model is perfect, but quite often a problem can be solved much easier if original design decisions are reviewed.

Another option is to completely ignore ServiceBase in most of the code and create a ServiceBaseAdapter for communication with the code that is not interface friendly. Such adapter can just call your interface methods when its method are called.

Try something like this:
List<object> collection = new List<object>();
foreach(var obj in collection.OfType<Base>().OfType<IBase>())
{
// Do what ever you want
}

C# Generics with 'Wildcards'

I'm looking for a way to get wildcards to work in .NET generics.
My code is as follows:
private class Rule<TSource, TSelected> where TSource : class where TSelected : class
{
// stuff in here
}
I want to be able to create a List<> of Rules where the TSource will be the same but the TSelected may be different.

You need to make a contravariant generic interface IRule<TSource, in TSelected> and make a list of that, where in addition TSelected is going to be constrained to some meaningful class. Constraining to any reference type as in your existing code will compile, but you won't be able to do anything meaningful with anything that has to do with TSelected.
At this time there is no other way to use variant generics (unless of course you go into reflection mode with List<dynamic> or something equivalent), so if this solution does not work for you you will need to redesign.

If I read your question right, I think you'd have to do this:
public interface ISelected
{
// ISelected interface
}
// A TSelected implementation
public class Implementation1: ISelected { }
// Another
public class Implementation2 : ISelected { }
// our Rule
private class Rule<TSource, TSelected> where TSource : class where TSelected ISelected
{
}

If the TSelected classes has the same super-class, you can just make a list of Rule<TSource, TSelectedSuperClass>. I believe you can use typeof (http://msdn.microsoft.com/en-us/library/58918ffs(v=vs.71).aspx) to get the exact subclass after reading the TSelected object again.
Alternatively you can make a container class to contain both and also store the exact types.
An interface could do it instead of a super class. If the Selected share implementation however, I prefer an abstract class.

Can I add a dynamic method to an interface in c#?

Can I add a dynamic method to an interface in c#?
So the interface method doesn't exist but exists on the underlying class and I want to call it via an interface.
thanks

That kind of defeats the point of an interface. If you want it on some of the classes and not others then you can implement it that way, but you will have to cast it to the known class type first.
You could probably use some reflection to check in the under-laying class type has the method you want to call if you want to be really fussy about it (and avoid knowing the type to cast)

Try making a new interface that implements the original interface as a sort of "middle man" between your class and the underlying interface
public interface IFoo
{
string PropA { get; set; }
}
public interface IFooExtended
{
void MyMethod();
}
public class ConcreteFoo : IFooExtended
{
// implementation...
}
It's not "dynamic" but this may help.

No - you could add an extension method to the interface to achieve a similar objective.

I think the right practice to follow that is as close as possible to what you're trying to achieve is create a new interface that inherits the old one.
Something like:
interface IMyInterface : IExistingInterface
{
void MyCustomMethod();
}
And you will address your new interface in your code. The classes implementing it will have your new method as well as the methods of the inherited interface.
You can't alter an existing interface, that would defeat the purpose of an interface itself.

If you're asking if you want to use a dynamic interface (e.g., strong-typed duck typing like in Visual Basic), then no, C# doesn't natively support this. But you can check out the Code Project article, Dynamic interfaces in any .NET language.

C# class design - what can I use instead of "static abstract"?

I want to do the following
public abstract class MyAbstractClass
{
public static abstract int MagicId
{
get;
}
public static void DoSomeMagic()
{
// Need to get the MagicId value defined in the concrete implementation
}
}
public class MyConcreteClass : MyAbstractClass
{
public static override int MagicId
{
get { return 123; }
}
}
However I can't because you can't have static abstract members.
I understand why I can't do this - any recommendations for a design that will achieve much the same result?
(For clarity - I am trying to provide a library with an abstract base class but the concrete versions MUST implement a few properties/methods themselves and yes, there are good reasons for keeping it static.)

You fundamentally can't make DoSomeMagic() work with the current design. A call to MyConcreteClass.DoSomeMagic in source code will be translated into MyAbstractClasss.DoSomeMagic in the IL. The fact that it was originally called using MyConcreteClass is lost.
You might consider having a parallel class hierarchy which has the same methods but virtual - then associate each instance of the original class with an instance of the class containing the previously-static members... and there should probably only be one instance of each of those.

Would the Singleton pattern work perhaps? A link to the MSDN article describing how to implement a singleton in C#:
http://msdn.microsoft.com/en-us/library/ff650316.aspx
In your particular example, the Singelton instance could extend an abstract base class with your MagicId in it.
Just a thought :)

I would question that there are "good reasons" for making the abstract members static.
If your thinking is that these members might reflect some property of the derived class itself rather than a given instance, this does not necessarily mean the members should be static.
Consider the IList.IsFixedSize property. This is really a property of the kind of IList, not any particular instance (i.e., any T[] is going to be fixed size; it will not vary from one T[] to another). But still it should be an instance member. Why? Because since multiple types may implement IList, it will vary from one IList to another.
Consider some code that takes any MyAbstractClass (from your example). If this code is designed properly, in most cases, it should not care which derived class it is actually dealing with. What matters is whatever MyAbstractClass exposes. If you make some abstract members static, basically the only way to access them would be like this:
int magicId;
if (concreteObject is MyConcreteClass) {
magicId = MyConcreteClass.MagicId;
} else if (concreteObject is MyOtherConcreteClass) {
magicId = MyOtherConcreteClass.MagicId;
}
Why such a mess? This is much better, right?
int magicId = concreteObject.MagicId;
But perhaps you have other good reasons that haven't occurred to me.

Your best option is to use an interface with MagicId only using a setter
public interface IMagic
{
int MagicId { get; }
}
By the nature of Static meaning there can only be one (yes like Highlander) you can't override them.
Using an interface assumes your client will implement the contract. If they want to have an instance for each or return the value of a Static variable it is up to them.
The good reason for keeping things static would also mean you do NOT need to have it overridden in the child class.

Not a huge fan of this option but...
You could declare the property static, not abstract, virtual and throw a NotImplementedException which returns an error message that the method has to be overridden in a derived class.
You move the error from compile time to run time though which is kinda ugly.

Languages that implement inheritance of static members do it through metaclasses (that is, classes are also objects, and these objects have a metaclass, and static inheritance exists through it). You can vaguely transpose that to the factory pattern: one class has the magic member and can create objects of the second class.
That, or use reflection. But you can't ensure at compile-time that a derived class implements statically a certain property.

Why not just make it a non-static member?

Sounds like a Monostate, perhaps? http://c2.com/cgi/wiki?MonostatePattern

The provider pattern, used by the ASP.NET membership provider, for example, might be what you're looking for.
You cannot have polymorphic behavior on static members, so you'll have a static class whose members delegate to an interface (or abstract class) field that will encapsulate the polymorphic behaviors.