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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.

how do i determine which class an interface contains

i have a set of classes that belong to an interface;
public class Platform : IGraphic
{
}
public class Decal : IGraphic
{
}
public class Character : IGraphic
{
}
public interface IGraphic
{
}
If i set an IGraphic value to point to say Decal like so;
IGraphic graphic = new Decal();
How can i, at some later point, determine which Class the Interface has been set to?

You can determine the implementation of an interface by using:
graphic.GetType()

First, classes do not belong to an interface, they can implement it.
Now, after we have defined it you can see that implementing the interface enables you to know that such methods are implemented in each class that implements the interface.
So your question is kind of backwards, you can implement the method differently for each class so you won't have to know what is the type of your object.
If you insist knowing the type you can use reflection.
I advice you using reflection as less as you can.
If you wan't to describe the purpose of your program maybe we can help you avoiding reflection (usually- a better architecture)

Use graphic.GetType().
This will get the Type of the instance.
Note that this works for every kind of object, not just for interfaces.
You could conceivably also use
if (graphic is Platform)
or
if (graphic is Decal)
etc.

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
}

Issue with List of generic classes

So I've got a generic class called VariableSeries, an abstract class called Indicator derived from it, and then various classes (let's call them indicators) that implement that abstract class. I want to have a List of indicators and be able to use it.
public class VariableSeries<T>
{
protected List<T> Series;
public int CurrentBar { get; private set; }
public T this[int index]
{
get
{
if (index > CurrentBar)
throw new Exception("Tried to look too far in the past, data does not exist.");
return Series[CurrentBar - index];
}
}
...
}
And I've got an Indicator class that's derived from VariableSeries:
public abstract class Indicator<T> : VariableSeries<T>
{
...
}
Now I want to have a List of indicators of various types. My first idea was to just declare a List, but that doesn't really work. And I can't just throw an interface at it and cast to that, because I need to use the indexation, which makes use of the generic type.
So let's say I've got the following indicator (one of many):
public class MovingAverage<T> : Indicator<double>
{
...
}
Is there any way to do the following:
List<???> Indicators = new List<???>();
Indicators.Add(new MovingAverage<type is provided dynamically>());
do stuff with Indicators[0][0];
Perhaps some sort of way of casting to a generic class without having to specify the type, like ((VariableSeries<>)Indicators[0])[0]?

The ??? in your List<???> must be a concrete type. This concrete type must, in your case, a commonly shared basetype or interface.
All your classes share a basetype VariableSeries<T> but this one is not concrete / specific. So List<VariableSeries<T>> is not possible.
If all your indicaters would use the generic type double, than you could use List<VariableSeries<double>>, but I am afraid that is not the case.
The question is: what are your going to do with that list? Iterate through them and then what? Ask for their value? What value? What type? A double? A string? The compiler cannot know!
One solution could be to create an interface like this:
public interface IVariableSeries
{
object this[int index] { get; }
}
Implement this interface EXPLICITLY in your VariableSeries<T> and use this interface as your concrete type in your list: List<IVariableSeries>.

You can make the abstract class implement an interface with all methods that will be common to all classes and has no type parameters.
class VariableSeries<T> : IUntypedInterface
Then you can use a List<IUntypedInterface> to get then all together.

You can do some stuff using reflection. For example you can create a MovingAverage with a dynamic T using the following:
Type dynamicType = typeof(int); // or any other, e.g. user selected type
var instance = (dynamic)Activator.CreateInstance(typeof(MovingAverage<>).CreateGenericType(dynamicType));
The problem of course is that you don't know the type of instance at compile time. Thus you can't call any methods on it and you can't cast it of course the type isn't known at compile time. That's why I wrapped it as dynamic. You can call any method and it will in the background reflect into that type and look for the method signature that you called.
You can check if instance is a MovingAverage<> by doing
typeof(MovingAverage<>).Equals(instance.GetType().GetGenericTypeDefinition())
Be aware that this will return false when instance is actually of a derived type of MovingAverage. You can also check that, but it's a bit more complicated.
Going the dynamic route is of course a dangerous path in a language that otherwise relies so much on static type checking. You won't have refactoring support and you will have to test a lot running your code. A single typo and your program will throw an exception.
Also, I would suggest you get familiar with .Net reflection. You're entering a dangerous world.

Add a generic method and pass the type to that method. this code will go in generic method.
List Indicators = new List();
Indicators.Add(new MovingAverage());

How can you require a constructor with no parameters for types implementing an interface?

Is there a way?
I need all types that implement a specific interface to have a parameterless constructor, can it be done?
I am developing the base code for other developers in my company to use in a specific project.
There's a proccess which will create instances of types (in different threads) that perform certain tasks, and I need those types to follow a specific contract (ergo, the interface).
The interface will be internal to the assembly
If you have a suggestion for this scenario without interfaces, I'll gladly take it into consideration...

Not to be too blunt, but you've misunderstood the purpose of interfaces.
An interface means that several people can implement it in their own classes, and then pass instances of those classes to other classes to be used. Creation creates an unnecessary strong coupling.
It sounds like you really need some kind of registration system, either to have people register instances of usable classes that implement the interface, or of factories that can create said items upon request.

You can use type parameter constraint
interface ITest<T> where T: new()
{
//...
}
class Test: ITest<Test>
{
//...
}

Juan Manuel said:
that's one of the reasons I don't understand why it cannot be a part of the contract in the interface
It's an indirect mechanism. The generic allows you to "cheat" and send type information along with the interface. The critical thing to remember here is that the constraint isn't on the interface that you are working with directly. It's not a constraint on the interface itself, but on some other type that will "ride along" on the interface. This is the best explanation I can offer, I'm afraid.
By way of illustration of this fact, I'll point out a hole that I have noticed in aku's code. It's possible to write a class that would compile fine but fail at runtime when you try to instantiate it:
public class Something : ITest<String>
{
private Something() { }
}
Something derives from ITest<T>, but implements no parameterless constructor. It will compile fine, because String does implement a parameterless constructor. Again, the constraint is on T, and therefore String, rather than ITest or Something. Since the constraint on T is satisfied, this will compile. But it will fail at runtime.
To prevent some instances of this problem, you need to add another constraint to T, as below:
public interface ITest<T>
where T : ITest<T>, new()
{
}
Note the new constraint: T : ITest<T>. This constraint specifies that what you pass into the argument parameter of ITest<T> must also derive from ITest<T>.
Even so this will not prevent all cases of the hole. The code below will compile fine, because A has a parameterless constructor. But since B's parameterless constructor is private, instantiating B with your process will fail at runtime.
public class A : ITest<A>
{
}
public class B : ITest<A>
{
private B() { }
}

Juan,
Unfortunately there is no way to get around this in a strongly typed language. You won't be able to ensure at compile time that the classes will be able to be instantiated by your Activator-based code.
(ed: removed an erroneous alternative solution)
The reason is that, unfortunately, it's not possible to use interfaces, abstract classes, or virtual methods in combination with either constructors or static methods. The short reason is that the former contain no explicit type information, and the latter require explicit type information.
Constructors and static methods must have explicit (right there in the code) type information available at the time of the call. This is required because there is no instance of the class involved which can be queried by the runtime to obtain the underlying type, which the runtime needs to determine which actual concrete method to call.
The entire point of an interface, abstract class, or virtual method is to be able to make a function call without explicit type information, and this is enabled by the fact that there is an instance being referenced, which has "hidden" type information not directly available to the calling code. So these two mechanisms are quite simply mutually exclusive. They can't be used together because when you mix them, you end up with no concrete type information at all anywhere, which means the runtime has no idea where to find the function you're asking it to call.

So you need a thing that can create instances of an unknown type that implements an interface. You've got basically three options: a factory object, a Type object, or a delegate. Here's the givens:
public interface IInterface
{
void DoSomething();
}
public class Foo : IInterface
{
public void DoSomething() { /* whatever */ }
}
Using Type is pretty ugly, but makes sense in some scenarios:
public IInterface CreateUsingType(Type thingThatCreates)
{
ConstructorInfo constructor = thingThatCreates.GetConstructor(Type.EmptyTypes);
return (IInterface)constructor.Invoke(new object[0]);
}
public void Test()
{
IInterface thing = CreateUsingType(typeof(Foo));
}
The biggest problem with it, is that at compile time, you have no guarantee that Foo actually has a default constructor. Also, reflection is a bit slow if this happens to be performance critical code.
The most common solution is to use a factory:
public interface IFactory
{
IInterface Create();
}
public class Factory<T> where T : IInterface, new()
{
public IInterface Create() { return new T(); }
}
public IInterface CreateUsingFactory(IFactory factory)
{
return factory.Create();
}
public void Test()
{
IInterface thing = CreateUsingFactory(new Factory<Foo>());
}
In the above, IFactory is what really matters. Factory is just a convenience class for classes that do provide a default constructor. This is the simplest and often best solution.
The third currently-uncommon-but-likely-to-become-more-common solution is using a delegate:
public IInterface CreateUsingDelegate(Func<IInterface> createCallback)
{
return createCallback();
}
public void Test()
{
IInterface thing = CreateUsingDelegate(() => new Foo());
}
The advantage here is that the code is short and simple, can work with any method of construction, and (with closures) lets you easily pass along additional data needed to construct the objects.

Call a RegisterType method with the type, and constrain it using generics. Then, instead of walking assemblies to find ITest implementors, just store them and create from there.
void RegisterType<T>() where T:ITest, new() {
}

I don't think so.
You also can't use an abstract class for this.

I would like to remind everyone that:
Writing attributes in .NET is easy
Writing static analysis tools in .NET that ensure conformance with company standards is easy
Writing a tool to grab all concrete classes that implement a certain interface/have an attribute and verifying that it has a parameterless constructor takes about 5 mins of coding effort. You add it to your post-build step and now you have a framework for whatever other static analyses you need to perform.
The language, the compiler, the IDE, your brain - they're all tools. Use them!

No you can't do that. Maybe for your situation a factory interface would be helpful? Something like:
interface FooFactory {
Foo createInstance();
}
For every implementation of Foo you create an instance of FooFactory that knows how to create it.

You do not need a parameterless constructor for the Activator to instantiate your class. You can have a parameterized constructor and pass all the parameters from the Activator. Check out MSDN on this.