interface as return type

问题

Can interface be a return type of a function. If yes then whats the advantage. e.g. is the following code correct where array of interface is being returned.

public interface Interface
{
    int Type { get; }
    string Name { get; }
}

public override Interface[] ShowValue(int a)
{
.
.

}

回答1:

Yes, you can return an interface.

Let's say classes A and B each implement interface Ic:

public interface Ic
{
    int Type { get; }
    string Name { get; }
}

public class A : Ic
{
     .
     .
     .
}

public class B : Ic
     .
     .
     .
}

public Ic func(bool flag)
{
     if (flag)
         return new A();
       return new B();

}

In this example func is like factory method — it can return different objects!

回答2:

Yes an interface is a very valid return value. Remember, you're not returning the definition of the interface, but rather an instance of that interface.

The benefit is very clear, consider the following code:

public interface ICar
{
    string Make { get; }
}

public class Malibu : ICar
{
    public string Make { get { return "Chevrolet"; } }
}

public class Mustang : ICar
{
    public string Make { get { return "Ford"; } }
}

now you could return a number of different ICar instances that have their own respective values.

But, the primary reason for using interfaces is so that they can be shared amongst assemblies in a well-known contract so that when you pass somebody an ICar, they don't know anything about it, but they know it has a Make. Further, they can't execute anything against it except the public interface. So if Mustang had a public member named Model they couldn't get to that unless it was in the interface.

回答3:

Yes it can.

The benefit is that you can abstract the return (and input) types.

public interface IFruit{ }

public class Apple: IFruit{}

public class Pear: IFruit{}

...

public function IFruit SelectRandomFromBasket(Basket<IFruit> basket){
  // this function can return Apple, Pear
}

回答4:

Yes it's possible, and it's a good thing for public functions.

For the why part of your question, I won't copy paste other people answers, so please refer to existing answers, for example:

List<T> or IList<T>
Method return an interface
https://stackoverflow.com/a/3564291/870604

来源：https://stackoverflow.com/questions/15392224/interface-as-return-type

标签

interface