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Specifying the return type of an abstract method from a Base Class according to a Sub Class

Asked 2009-03-24T01:26:40.517
19

I have the following structure: 

abstract class Base {
        public abstract List<...> Get(); //What should be the generic type?
}

class SubOne : Base {
    public override List<SubOne> Get() {

    }
}

class SubTwo : Base {
    public override List<SubTwo> Get() {

    }
}

I want to create an abstract method that returns whatever class the concrete sub class is. So, as you can see from the example, the method in SubOne should return List<SubOne> whereas the method in SubTwo should return List<SubTwo>.

What type do I specify in the signature declared in the Base class ?

[UPDATE]

Thank you for the posted answers.

The solution is to make the abstract class generic, like such:

abstract class Base<T> {
        public abstract List<T> Get();
}

class SubOne : Base<SubOne> {
    public override List<SubOne> Get() {

    }
}

class SubTwo : Base<SubTwo> {
    public override List<SubTwo> Get() {

    }
}
c# generics polymorphism abstract-class overriding
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2 Answers

37

Your abstract class should be generic.

abstract class Base<T> {
        public abstract List<T> Get(); 
}

class SubOne : Base<SubOne> {
    public override List<SubOne> Get() {

    }
}

class SubTwo : Base<SubTwo> {
    public override List<SubTwo> Get() {
    }
}

If you need to refer to the abstract class without the generic type argument, use an interface:

interface IBase {
        //common functions
}

abstract class Base<T> : IBase {
        public abstract List<T> Get(); 
}
answered 2009-03-24T01:32:55.947
4
public abstract class Base<T> 
{       
    public abstract List<T> Get(); 
}

class SubOne : Base<SubOne> 
{
    public override List<SubOne> Get() { return new List<SubOne>(); }
}

class SubTwo : Base<SubTwo> 
{
    public override List<SubTwo> Get() { return new List<SubTwo>(); }
}
answered 2009-03-24T01:34:28.517

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