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Passing inherited class

I'm trying some simple code to understand the generics in C#. The purpose of the code here is to have a trainer that has her own animal and will ask it to do various stuff (for the sake of the example, to jump).
The problem is with the constructor of the trainer. I would like to be able to pass a Dog, or a Cat. They both inherit from the same class, but because I specified the type definition it seems I can't pass them as argument, they can't be both valid. Is there a way to specify a generic class like "Animal" so I could pass a dog or a cat and keep it as a member?
class AnimalDefinition
{
public Fur Fur;
}
class DogDefinition : AnimalDefinition
{
public BarkSound Bark;
}
class CatDefinition : AnimalDefinition
{
public MeowSound Meow;
}
class Animal<TDefinition> where TDefinition : AnimalDefinition
{
public TDefinition Definition;
public void Jump()
{
Console.WriteLine("Jump.");
}
}
class Dog : Animal<DogDefinition>
{
public Dog(DogDefinition def)
{
Definition = def;
}
}
class Cat : Animal<CatDefinition>
{
public Cat(CatDefinition def)
{
Definition = def;
}
}
class Trainer
{
Animal _animal;
public Trainer(Animal myAnimal)
{
_animal = myAnimal;
}
public MakeJump()
{
_animal.Jump();
}
public Listen()
{
// if T is DogDefinition hear barking
// else if T is CatDefinition hear a meowing, etc
}
}
EDIT: Additional question following Chris Berger's answer (which works, but I didn't change the code to keep the question/answer logical). I added a definition member in the Animal class. Is there any way I can access Bark or Meow from inside the Trainer class or will I have to derivate the class Trainer with CatTrainer : Trainer<CatDefinition>? That is, is there something similar to what we have with classes,
if(T is CatDefinition)
{ // Meowing}
else
{}

I think I agree with the first commenter, that you don't necessarily want generics for this, but assuming you have some other reason for wanting generics...
The solution here is to create a class Animal, which Animal<T> derives from.
For example:
public class Animal
{
public virtual void Jump()
{
Console.WriteLine("Jump.");
}
}
public class Animal<T> : Animal where T : AnimalDefinition
{
public override void Jump()
{
//you can override Jump here if you want to
}
}
public class Dog : Animal<DogDefinition> {}
public class Cat : Animal<CatDefinition> {}
Or, actually, a second option is to give Trainer visibility to the generic parameter:
public class Animal<T> where T : AnimalDefinition
{
public void Jump()
{
Console.WriteLine("Jump.");
}
}
public class Dog : Animal<DogDefinition> {}
public class Cat : Animal<CatDefinition> {}
public class Trainer<T> where T : AnimalDefinition
{
Animal<T> _animal;
public Trainer(Animal<T> myAnimal)
{
_animal = myAnimal;
}
public MakeJump()
{
_animal.Jump();
}
}
And as a tangent... this might be a good place to use a self-referential generic.
public class Animal<T> where T : Animal<T> { }
public class Dog : Animal<Dog> { }
Here's a little more reading on that pattern: https://blogs.msdn.microsoft.com/simonince/2008/06/12/generics-the-self-referencing-generics-pattern/

Polymorphic Downcasting in c#?

I'm trying to make food for my IAnimals using a FoodFactory and have a large List<IAnimal> of Dogs and Foxs etc. Ideally, I would pass in an IAnimal and the FoodFactory would return the right food but I am not sure how to do this.
interface IAnimal {
void MakeNoise();
}
public sealed class Dog : IAnimal {
public void MakeNoise() { Console.WriteLine("Woof woof"); }
}
public sealed class Fox : IAnimal {
public void MakeNoise() { Console.WriteLine("What does the fox say?"); }
}
public static class FoodFactory {
public static void Create(Dog dog) {
Console.WriteLine("return dog food");
}
public static void Create(Fox fox) {
Console.WriteLine("return fox food");
}
}
and here's my caller code:
var myList = new List<IAnimal> { new Dog(), new Fox() };
foreach (var animal in myList)
{
FoodFactory.Create(animal); // Sadly, this doesn't work
}
Is there a 'proper' way to do this? All I can think of is a load of if statements like:
if (animal is Dog) { FoodFactory.Create(animal as Dog); }
I have a lot of animals and I'd much rather the computer work out which one it's dealing with than me! Thank you.
UPDATE
Thank you to all that have posted. I went with Xinchao's answer because it was most applicable in my context; it didn't affect my animal classes and allowed the type to be resolved at runtime without me checking all the animal types. There were three helpful answers which would have worked (e.g. using visitor pattern) but they weren't quite applicable in my context as I don't want to change/extend my animals.

The reason you are having this problem is the so-called overload resolution happens at compile time instead of run-time.
There are a couple of ways to solve it:
Using a bunch of if-else-if statements is certainly one way, although you can write it prettier.
With .Net 4.0 or above, you can use to "dynamic" keyword to delay the overload resolution to run-time. It has a performance penalty, but it achieves accurately what you need:
public static class FoodFactory {
public static void Create(dynamic animal) {
InternalCreate (animal);
}
private static void InternalCreate (Dog dog) {
Console.WriteLine("return dog food");
}
private static void InternalCreate (Fox fox) {
Console.WriteLine("return fox food");
}
}
To add a bit more type safety, you might consider to do something like:
public static class FoodFactory {
public static void Create(IAnimal animal) {
Dispatch (animal);
}
private static void Dispatch (dynamic animal) {
InternalCreate (animal);
}
private static void InternalCreate (Dog dog) {
Console.WriteLine("return dog food");
}
private static void InternalCreate (Fox fox) {
Console.WriteLine("return fox food");
}
}

Your FoodFactory does need to know what kind of animal its feeding, but I would imagine that the animal itself knows what kind of food it wants to eat. What if IAnimal provided that?
interface IAnimal {
void MakeNoise();
FoodType FavoriteFood { get; }
}
public sealed class Dog : IAnimal {
public void MakeNoise() { Console.WriteLine("Woof woof"); }
public FoodType FavoriteFood { get { return FoodType.DogFood; } }
}
public sealed class Fox : IAnimal {
public void MakeNoise() { Console.WriteLine("What does the fox say?"); }
public FoodType FavoriteFood { get { return FoodType.WhatTheFoxEats; } }
}
Now your FoodFactory has the information it needs to build food:
public static class FoodFactory {
public static IFood Create(IAnimal animal) {
// animal.FavoriteFood tells you what food to make
}
}
Maybe FavoriteFood actually returns an instance of food, and the factory just delegates to that? Maybe the factory maintains a mapping or some other logic of the enum above to actual food instances? Maybe some other way? (Or maybe you just output to the console like you already are instead of returning an object like I'm trying to do, in which case the animals can just write to the console and the factory still doesn't need to know anything else about the animal.) In any event, the factory's relationship to the animal is now polymorphically defined.

I think you need to modify your Create method in FoodFactory class to accept IAnimal as a parameter instead. You would also need to have a method declaration for FavFood or whatever you want to call it in the Interface which would get specific implementation from classes (Dogs, Fox) that inherits the Interface. Then in a factory class you could supply any animal of type IAnimal and have a method that invokes Animal specific FavFood method.
interface IAnimal
{
void FavFood();
}
public sealed class Dog : IAnimal
{
public void FavFood() { Console.WriteLine("Me loves dog food. Woof woof."); }
}
public sealed class Goat : IAnimal
{
public void FavFood() { Console.WriteLine("Me loves goat food. myaaa.."); }
}
public static class FoodFactory
{
public static void Create(IAnimal animal)
{
animal.FavFood();
}
}
And when you call it, you would do
var animals = new List<IAnimal> { new Dog(), new Fox() };
foreach (var animal in animals)
{
FoodFactory.Create(animal);
}
Did I answer what you were looking for? If not, let me know where I missed it...

Another alternative would be to use the visitor pattern:
using System;
using System.Collections.Generic;
public interface IAnimalVisitor
{
void Visit(Dog dog);
void Visit(Fox fox);
}
public class FeedingPersonnel : IAnimalVisitor
{
public void Visit(Dog dog)
{
Console.WriteLine("return dog food");
}
public void Visit(Fox fox)
{
Console.WriteLine("return fox food");
}
}
//public class Veterinarian : IAniamalVisitor { ... } (if you need it)
interface IAnimal
{
void Accept( IAnimalVisitor visitor);
void MakeNoise();
}
public sealed class Dog : IAnimal {
public void Accept( IAnimalVisitor visitor) { visitor.Visit(this); }
public void MakeNoise() { Console.WriteLine("Woof woof"); }
}
public sealed class Fox : IAnimal {
public void Accept( IAnimalVisitor visitor) { visitor.Visit(this); }
public void MakeNoise() { Console.WriteLine("What does the fox say?"); }
}
public class Test
{
public static void Main()
{
var myList = new List<IAnimal> { new Dog(), new Fox() };
var feeder = new FeedingPersonnel();
foreach (var animal in myList)
{
animal.Accept(feeder);
}
}
}
This method avoids casting and also provides you the means to add another types of visitors. With the downside that you have to provide Visit once for each new Animal and add a new method to the IAnimalVisitor and define it in each visitor implementer whenever a new Animal is added.
Depending on you actual situation this might be acceptable (or not).

Avoid explicit type casting when overriding inherited methods

I have a base abstract class that also implements a particular interface.
public interface IMovable<TEntity, T>
where TEntity: class
where T: struct
{
TEntity Move(IMover<T> moverProvider);
}
public abstract class Animal : IMovable<Animal, int>
{
...
public virtual Animal Move(IMover<int> moverProvider)
{
// performs movement using provided mover
}
}
Then I have inherited classes some of which have to override interface implementation methods of the base class.
public class Snake : Animal
{
...
public override Animal Move(IMover<int> moverProvider)
{
// perform different movement
}
}
My interface methods return the same object instance after it's moved so I can use chaining or do something directly in return statement without using additional variables.
// I don't want this if methods would be void typed
var s = GetMySnake();
s.Move(provider);
return s;
// I don't want this either if at all possible
return (Snake)GetMySnake().Move(provider);
// I simply want this
return GetMySnake().Move(provider);
Question
As you can see in my example my overrides in child class returns base class type instead of running class. This may require me to cast results, which I'd like to avoid.
How can I define my interface and implementations so that my overrides will return the actual type of the executing instance?
public Snake Move(IMover<int> moverProvider) {}

I suggest changing the return type of the interface method to void and moving the chaining behaviour to an extension method where you can get the real type of the target e.g.
public interface IMovable<TEntity, T>
where TEntity : class
where T : struct
{
void MoveTo(IMover<T> moverProvider);
}
public abstract class Animal : IMovable<Animal, int>
{
public virtual void MoveTo(IMover<int> mover) { }
}
public static class AnimalExtensions
{
public static TAnimal Move<TAnimal>(this TAnimal animal, IMover<int> mover) where TAnimal : Animal, IMovable<TAnimal, int>
{
animal.MoveTo(mover);
return animal;
}
}
Note you can make the Move extension more generic if you need it to apply more generally:
public static TEntity Move<TEntity, T>(this TEntity entity, IMover<T> mover) where TEntity : IMovable<TEntity, T> where T : struct
{
entity.MoveTo(mover);
return entity;
}

You can convert Animal to a generic type that accepts the concrete type as a type parameter:
public abstract class Animal<T> : IMovable<T, int> where T:Animal<T>
{
public virtual T Move(IMover<int> moverProvider)
{
...
}
}
public class Snake : Animal<Snake>
{
public override Snake Move(IMover<int> moverProvider)
{
...
}
}

How about:
public virtual T Move<T>(IMover<int> moverProvider) where T : Animal
{
// performs movement using provided mover
}

Sometimes you need to have current type as method return value and it has to change in derived classes. I'd avoid this pattern because it'll lead to strange behaviors and unusual syntax (if your model becomes complex) but give it a try (primary because for very small hierarchies it looks pretty simple):
abstract class Animal<TConcrete> : IMovable<TConcrete, int>
where TConcrete : Animal<T>
{
public virtual T Move(IMover<int> moverProvider) {
return (T)this; // Cast to Animal<T> to T isn't implicit
}
}
sealed class Snake : Animal<Snake>
{
public virtual Snake Move(IMover<int> moverProvider) {
return this;
}
}
Why is this bad? You can answer yourself when you'll need to declare a generic variable of type Animal<TConcrete> (in practice this stops you to have a variable with that base class).
What I'd do is to make this requirement clear (with a class or an extension method - in this case using another name):
abstract class Animal : IMovable<Animal, int>
{
// Please note that this implementation is explicit
Animal IMovable<Animal, int>.Move(IMover<int> moverProvider) {
return MoveThisAnimal(moverProvider);
}
protected virtual Animal MoveThisAnimal(IMover<int> moverProvider) {
// Peform moving
return this;
}
}
class Snake : Animal
{
public Snake Move(IMover<int> moverProvider) {
return (Snake)MoveThisAnimal(moverProvider);
}
protected override Animal MoveThisAnimal(IMover<int> moverProvider) {
// Peform custom snake moving
return this;
}
}

It's messy, but by introducing a non-generic base interface, an extension method can give the desired result. It can also be simplified (to remove the second explicit interface implementation) if you don't care about exposing the 'MoveFunc' to callers:
public interface IMovable
{
IMovable MoveFunc();
}
public interface IMovable<TEntity, T> : IMovable
where TEntity : IMovable
{
new TEntity MoveFunc();
}
public abstract class Animal : IMovable<Animal, int>
{
protected virtual Animal MoveFunc()
{
// performs movement using provided mover
Debug.WriteLine("Animal");
}
Animal IMovable<Animal, int>.MoveFunc()
{
return MoveFunc();
}
IMovable IMovable.MoveFunc()
{
return ((IMovable<Animal, int>)this).MoveFunc();
}
}
public class Snake : Animal
{
protected override Animal MoveFunc()
{
// performs movement using provided mover
Debug.WriteLine("Snake");
}
}
public static class IMovableExtensions
{
public static TOut Move<TOut>(this TOut entity) where TOut : IMovable
{
return (TOut)entity.MoveFunc();
}
}
...
Snake snake = new Snake();
Snake moved = snake.Move(); // "Snake"
Animal animal = snake;
animal.Move() // "Snake"

C# - using extension methods to provide default interface implementation

I'm just learning about C# extension methods, and was wondering if I can use it to provide a default implementation for an interface.
Say:
public interface Animal {
string MakeSound();
}
public static string MakeSound(this Animal) {
return "";
}
Then
public class Dog : Animal {
string MakeSound() {
return "Bark";
}
}
public class Porcupine : Animal {
}
And last:
Animal dog = new Dog();
Animal porcupine = new Porcupine();
Print(dog.MakeSound());
Print(porcupine.MakeSound());
I'd like the porcupine and any other animals that have not explicitly implemented MakeSound to use the default extension method that returns an empty string, but dog and any animal that does have an explicit implementation return its own implementation such as "Bark".
So my questions:
1. Is this doable?
2. If not, is there any other way to implement default behavior for an interface?
Abstract class instead of interface is not an option because C# doesn't support multiple inheritance and my classes are inheriting behavior of another class.

I'd generally recommend a base class, however, if that's out, you can do something like this:
public interface IAnimal { }
public interface INoisyAnimal : IAnimal {
string MakeSound();
}
public static class AnimalExtensions {
public static string MakeSound(this IAnimal someAnimal) {
if (someAnimal is INoisyAnimal) {
return (someAnimal as INoisyAnimal).MakeSound();
}
else {
return "Unknown Noise";
}
}
}
public class Dog : INoisyAnimal {
public string MakeSound() {
return "Bark";
}
}
public class Porcupine : IAnimal { }
This makes every IAnimal look like a INoisyAnimal even if it isn't really one. For example:
IAnimal dog = new Dog();
IAnimal porcupine = new Porcupine();
Console.WriteLine(dog.MakeSound()); // bark
Console.WriteLine(porcupine.MakeSound()); // Unknown Noise
However, this still isn't an actual implementation of the interface. Notice that despite appearances
Console.WriteLine(porcupine is INoisyAnimal); // false
Another option might be to create a wrapper to extend your base class when new functionality is needed:
public class NoisyAnimalWrapper : INoisyAnimal {
private readonly IAnimal animal;
public NoisyAnimalWrapper(IAnimal animal) {
this.animal = animal;
}
public string MakeSound() {
return "Unknown Noise";
}
}
public static class AnimalExtensions {
public static INoisyAnimal Noisy(this IAnimal someAnimal) {
return someAnimal as INoisyAnimal ??
new NoisyAnimalWrapper(someAnimal);
}
}
Then you can create a INoisyAnimal from any IAnimal whenever you need to:
INoisyAnimal dog = new Dog();
INoisyAnimal porcupine = new Porcupine().Noisy();
Console.WriteLine(dog.MakeSound()); // bark
Console.WriteLine(porcupine.MakeSound()); // Unknown Noise
You could also make the wrapper generic (e.g. NoisyAnimal<T> where T : IAnimal, new) and get rid of the extension method altogether. Depending on your actual use case, this may be preferable to the previous option.

I don't know exactly what is your real case or if you are just experimenting but, if only some animals are noisy, then it might a good case for Interface segregation.
For example:
public class Dog : IAnimal, INoisy
{
public string MakeSound()
{
return "Bark";
}
}
public class Porcupine : IAnimal
{
}
Then, you will only call MakeSound or objects that are actually noisy.

How about something like this? It allows you to avoid having a base class, and you can do what you had in mind, right?
public interface Animal
{
// Fields
string voice { get; }
}
public static class AnimalHelper
{
// Called for any Animal
public static string MakeSound(this Animal animal)
{
// Common code for all of them, value based on their voice
return animal.voice;
}
}
public class Dog : Animal
{
public string voice { get { return "Woof!"; } }
}
public class Purcupine : Animal
{
public string voice { get { return ""; } }
}

C# Generics: wildcards

I'm new to the c# world, and I'm trying to wrap my head around generics. Here is my current problem:
public Interface IAnimal{
string getType();
}
public Interface IAnimalGroomer<T> where T:IAnimal{
void groom(T);
}
Now I want to have a dictionary that contains these animal groomers. How do I do that? In java, I could do something like this:
HashMap<String,IAnimalGroomer<?>> groomers = new HashMap<>();
Edit: Here is an example of what I'm trying to do:
public class Dog : IAnimal
{
public string GetType()
{
return "DOG";
}
public void ClipNails() { }
}
public class DogGroomer : IAnimalGroomer<Dog>
{
public void Groom(Dog dog)
{
dog.ClipNails();
}
}
public class Program
{
private List<IAnimalGroomer<IAnimal>> groomers = new List<IAnimalGroomer<IAnimal>>();
public void doSomething()
{
//THIS DOESN"T COMPILE!!!!
groomers.Add(new DogGroomer());
}
}
EDIT
I think my intentions were unclear in the original post. My ultimate goal is to make an AnimalGroomerClinic that employs different types of IAnimalGroomers. Then animal owners can drop off animals at the clinic, and the clinic can decide which groomer should take care of the animal:
public class AnimalGroomerClinic
{
public Dictionary<String, IAnimalGroomer> animalGroomers = new Dictionary<String,IAnimalGroomer>();
public void employGroomer(IAnimalGroomer groomer){
animalGroomers.add(groomer.getAnimalType(), groomer);
}
public void Groom(IAnimal animal){
animalGroomers[animal.getAnimalType()].Groom(animal);
}
}
I realize I could do this without using generics. But the generics allow me to write the IAnimalGroomer interface in such a way that it is tied (at compile time) to a specific instance of IAnimal. In addition, concrete classes of IAnimalGroomer don't need to cast their IAnimals all the time, since generics would force implementations to deal with one specific kind of animal. I have used this idiom before in Java, and I'm just wondering if there is a similar way to write it in C#.
Edit 2:
Lots of interesting discussion. I'm accepting an answer that pointed me to dynamic dispatching in the comments.

What you want is call site covariance, which is not a feature that C# supports. C# 4 and above support generic variance, but not call site variance.
However, that doesn't help you here. You want a dog groomer to be put in a list of animal groomers, but that can't work in C#. A dog groomer cannot be used in any context in which an animal groomer is needed because a dog groomer can only groom dogs but an animal groomer can also groom cats. That is, you want the interface to be covariant when it cannot be safely used in a covariant manner.
However your IAnimalGroomer<T> interface could be contravariant as it stands: an animal groomer can be used in a context in which a dog groomer is required, because an animal groomer can groom dogs. If you made IAnimalGroomer<T> contravariant by adding in to the declaration of T then you could put an IAnimalGroomer<IAnimal> into an IList<IAnimalGroomer<Dog>>.
For a more realistic example, think of IEnumerable<T> vs IComparer<T>. A sequence of dogs may be used as a sequence of animals; IEnumerable<T> is covariant. But a sequence of animals may not be used as a sequence of dogs; there could be a tiger in there.
By contrast, a comparer that compares animals may be used as a comparer of dogs; IComparer<T> is contravariant. But a comparer of dogs may not be used to compare animals; someone could try to compare two cats.
If that is still not clear then start by reading the FAQ:
http://blogs.msdn.com/b/csharpfaq/archive/2010/02/16/covariance-and-contravariance-faq.aspx
and then come back and ask more questions if you have them.

There are two interfaces, IEnumerable and IEnumerable<T> which are close to what you are trying to accomplish. So you can have a dictionary like Dictionary<string,IEnumerable> which can contain as values IEnumerable<int>, IEnumerable<string>, etc. The trick here is to derive IAnimalGroomer<T> from IAnimalGroomer, a non generic interface.
EDIT:
As an example, per your request, after creating an interface called IAnimalGroomer with:
public interface IAnimalGroomer{
}
, if you change the line that reads:
public interface IAnimalGroomer<T> where T:IAnimal{
to
public interface IAnimalGroomer<T> : IAnimalGroomer where T:IAnimal{
and the line that reads:
private List<IAnimalGroomer<IAnimal>> groomers = new List<IAnimalGroomer<IAnimal>>();
to
private List<IAnimalGroomer> groomers=new List<IAnimalGroomer>();
your code should compile and work.

I know this has been Lipperted but I still feel like answering. The List is a red herring here, it doesn't matter that you're using it.
The reason this doesn't work is because IAnimalGroomer<T> itself is not covariant, and it can't be made covariant explicitly because of the groom(T) method. It is illegal to cast IA<Derived> to IA<Base> in the general case, or in different words, generic interfaces are not covariant by default. The List<T>.Add method is what triggers a cast from DogGroomer (which is IAnimalGroomer<Dog>) to IAnimalGroomer<IAnimal>, but for example, this still won't work:
IAnimalGroomer<Dog> doggroomer = new DogGroomer(); // fine
IAnimalGroomer<IAnimal> animalgroomer = doggroomer; // invalid cast, you can explicitly cast it
// in which case it fails at run time
If this worked (so if IAnimalGroomer<T> was covariant), you could in fact also add a DogGroomer to your list, despite the List<T> not being covariant! That's why I said the list is a red herring.
The reason generic interface covariance isn't the default is because of type safety. I added Cat/CatGroomer classes to your code that are basically the same as the ones for dogs. Look at the main function and the comments in it.
public interface IAnimal
{
string getType();
}
public interface IAnimalGroomer<T> where T:IAnimal
{
void groom(T t);
}
public class Dog : IAnimal
{
public string getType() { return "DOG"; }
public void clipNails() { }
}
public class DogGroomer : IAnimalGroomer<Dog>
{
public void groom(Dog dog)
{
dog.clipNails();
}
}
public class Cat : IAnimal
{
public string getType() { return "CAT"; }
public void clipNails() { }
}
public class CatGroomer : IAnimalGroomer<Cat>
{
public void groom(Cat cat)
{
cat.clipNails();
}
}
public class Program
{
static void Main(string[] args)
{
// this is fine.
IAnimalGroomer<Dog> doggroomer = new DogGroomer();
// this is an invalid cast, but let's imagine we allow it!
IAnimalGroomer<IAnimal> animalgroomer = doggroomer;
// compile time, groom parameter must be IAnimal, so the following is legal, as Cat is IAnimal
// but at run time, the groom method the object has is groom(Dog dog) and we're passing a cat! we lost compile-time type-safety.
animalgroomer.groom(new Cat());
}
}
There are no sequences used, yet the code would still break type safety if it was legal.
This type of cast could be allowed, but the errors caused by it would happen at run-time, which I imagine was not desirable.
If you mark the type parameter T as "out", then you can cast A<Derived> into A<Base>. However, you can no longer have a method with T as an argument, which you do. But it eliminates the problem of trying to shove a Cat into a Dog.
IEnumerable<T> is an example of a covariant interface - it has no f(T) methods so the problem can't happen, unlike with your groom(T) method.

As Brian pointed out in comments above, maybe dynamic is the way to go here.
Check out the following code. You get the benefits of generics to tie down the API nicely and under the hoods you use dynamic to make things work.
public interface IAnimal
{
}
public class Dog : IAnimal
{
}
public class Cat : IAnimal
{
}
public class BigBadWolf : IAnimal
{
}
//I changed `IAnimalGroomer` to an abstract class so you don't have to implement the `AnimalType` property all the time.
public abstract class AnimalGroomer<T> where T:IAnimal
{
public Type AnimalType { get { return typeof(T); } }
public abstract void Groom(T animal);
}
public class CatGroomer : AnimalGroomer<Cat>
{
public override void Groom(Cat animal)
{
Console.WriteLine("{0} groomed by {1}", animal.GetType(), this.GetType());
}
}
public class DogGroomer : AnimalGroomer<Dog>
{
public override void Groom(Dog animal)
{
Console.WriteLine("{0} groomed by {1}", animal.GetType(), this.GetType());
}
}
public class AnimalClinic
{
private Dictionary<Type, dynamic> groomers = new Dictionary<Type, dynamic>();
public void EmployGroomer<T>(AnimalGroomer<T> groomer) where T:IAnimal
{
groomers.Add(groomer.AnimalType, groomer);
}
public void Groom(IAnimal animal)
{
dynamic groomer;
groomers.TryGetValue(animal.GetType(), out groomer);
if (groomer != null)
groomer.Groom((dynamic)animal);
else
Console.WriteLine("Sorry, no groomer available for your {0}", animal.GetType());
}
}
And now you can do:
var animalClinic = new AnimalClinic();
animalClinic.EmployGroomer(new DogGroomer());
animalClinic.EmployGroomer(new CatGroomer());
animalClinic.Groom(new Dog());
animalClinic.Groom(new Cat());
animalClinic.Groom(new BigBadWolf());
I'm not sure if this is somewhat what you were looking for. Hope it helps!

Here is some code that works. I've added some classes and switch AnimalGroomer to be an abstract class not an interface:
class Program
{
static void Main(string[] args)
{
var dict = new Dictionary<string, IGroomer>();
dict.Add("Dog", new DogGroomer());
// use it
IAnimal fido = new Dog();
IGroomer sample = dict["Dog"];
sample.Groom(fido);
Console.WriteLine("Done");
Console.ReadLine();
}
}
// actual implementation
public class Dog : IAnimal { }
public class DogGroomer : AnimalGroomer<Dog>
{
public override void Groom(Dog beast)
{
Console.WriteLine("Shave the beast");
}
}
public interface IAnimal {
}
public interface IGroomer
{
void Groom(object it);
}
public abstract class AnimalGroomer<T> : IGroomer where T : class, IAnimal
{
public abstract void Groom(T beast);
public void Groom(object it)
{
if (it is T)
{
this.Groom(it as T);
return;
}
throw new ArgumentException("The argument is not a " + typeof(T).GetType().Name);
}
}
Please let me know if there are any questions

From my understanding, you cannot put the type constraints in the parameter in this case. which means you might need to do the boxing and unboxing. you might need to use a normal interface.
public interface IAnimal{
string GetType();
}
public interface IAnimalGroomer{
void Groom(IAnimal dog);
}
public class Dog : IAnimal
{
public string GetType()
{
return "DOG";
}
public void ClipNails()
{
}
}
public class DogGroomer : IAnimalGroomer
{
public void Groom(IAnimal dog)
{
if (dog is Dog)
{
(dog as Dog).ClipNails();
}
else {
// something you want handle.
}
}
}
public class Program
{
private List<IAnimalGroomer> groomers = new List<IAnimalGroomer>();
public void doSomething()
{
groomers.Add(new DogGroomer());
}
}
Or maybe you need to have another technical design for solving your problem

I'm adversed to using dynamic, because it has a runtime cost to it.
One simpler solution, uses a Dictionary<string, object> in which you can safely store any IAnimalGroomer<T>.
public class AnimalGroomerClinic {
public Dictionary<string, object> animalGroomers = new Dictionary<string, object>();
public void employGroomer<T>(IAnimalGroomer<T> groomer) where T : IAnimal {
animalGroomers.Add(groomer.getAnimalType(), groomer);
}
public void Groom<T>(T animal) where T : IAnimal {
// Could also check here if the 'as' operator returned null,
// which might happen if you don't have the specific groomer
(animalGroomers[animal.getAnimalType()] as IAnimalGroomer<T>).groom(animal);
}
}
Now, this requires a cast, which you might say is unsafe. But you know it's safe due to encapsulation. If you put an IAnimalGroomer<Dog> into the hashmap under the key "dog". And request it again with the key "dog", you know it will still be an IAnimalGroomer<Dog>.
Just like with the java equivalent:
class AnimalGroomerClinic {
public Map<String, Object> animalGroomers = new HashMap<>();
public <T extends IAnimal> void employGroomer(IAnimalGroomer<T> groomer) {
animalGroomers.put(groomer.getAnimalType(), groomer);
}
#SuppressWarnings("unchecked")
public <T extends IAnimal> void Groom(T animal) {
((IAnimalGroomer<T>) animalGroomers.get(animal.getAnimalType())).groom(animal);
}
}
Which still requires an unchecked cast (even if you change Object to IAnimalGroomer<?>). The point is that you're trusting your encapsulation enough to do an unchecked cast.
It doesn't really add anything to have IAnimalGroomer<?> instead of Object in terms of type safety. Because you're encapsulation already ensures more.
It could be done for readability, to indicated what kind of objects the map holds by having IAnimalGroomer<T> implement a stub interface:
public interface IAnimalGroomerSuper {
// A stub interface
}
public interface IAnimalGroomer<T> : IAnimalGroomerSuper where T : IAnimal {...}
Then the dictionary could be:
public Dictionary<string, IAnimalGroomerSuper> animalGroomers = ...;

The point is to use a non-generic interface behind the scenes to limit the types, but only expose the generic version.
void Main()
{
var clinic = new AnimalClinic();
clinic.Add(new CatGroomer());
clinic.Add(new DogGroomer());
clinic.Add(new MeanDogGroomer());
clinic.Groom(new Cat()); //Purr
clinic.Groom(new Dog()); //Woof , Grrr!
}
public interface IAnimal {}
public interface IGroomer {}
public class Dog : IAnimal
{
public string Woof => "Woof";
public string Growl => "Grrr!";
}
public class Cat : IAnimal
{
public string Purr => "Purr";
}
public interface IGroomer<T> : IGroomer where T : IAnimal
{
void Groom(T animal);
}
public class DogGroomer : IGroomer<Dog>
{
public void Groom(Dog dog) => Console.WriteLine(dog.Woof);
}
public class MeanDogGroomer : IGroomer<Dog>
{
public void Groom(Dog dog) => Console.WriteLine(dog.Growl);
}
public class CatGroomer : IGroomer<Cat>
{
public void Groom(Cat cat) => Console.WriteLine(cat.Purr);
}
public class AnimalClinic
{
private TypedLookup<IGroomer> _groomers = new TypedLookup<IGroomer>();
public void Add<T>(IGroomer<T> groomer) where T : IAnimal
=> _groomers.Add<T>(groomer);
public void Groom<T>(T animal) where T : IAnimal
=> _groomers.OfType<T, IGroomer<T>>().ToList().ForEach(g => g.Groom(animal));
}
public class TypedLookup<T> : Dictionary<Type, IList<T>>
{
public void Add<TType>(T item)
{
IList<T> list;
if(TryGetValue(typeof(TType), out list))
list.Add(item);
else
this[typeof(TType)] = new List<T>{item};
}
public IEnumerable<TRet> OfType<TType, TRet>() => this[typeof(TType)].Cast<TRet>();
public TRet First<TType, TRet>() => this[typeof(TType)].Cast<TRet>().First();
}