CODEWITHSUNDEEP
c#
Commonaught
Commonaught

Reputation: 340

Declare generic list as member of parent class

I want to create a parent class that contains a list and can do simple operations on that list (add, remove, or swap items). The type of object in the list will be different for each child class. If I make it a List<object> then I think I will have to do a bunch of casting in the child class (something that would be nice to avoid). Is there any way to accomplish this?

public abstract class Parent {
    
    protected List<T> ListOfSomeType; // <- List<T> isn't allowed
    
    protected void RemoveThing<T> (T thing) {
        ListOfSomeType.Remove(thing)
    }
    
    protected void AddThing<T> (T thing) {
        ListOfSomeType.Add(thing);
    }

    protected void SwapThings(int index1, int index2) {
        var temp = ListOfSomeType[index1];
        ListOfSomeType[index1] = ListOfSomeType[index2]
        ListOfSomeType[index2] = temp;
    }
}

public class Child1 : Parent {
    
    public Child() {
        ListOfSomeType = new List<SomeType>();
    }
}

public class Child2 : Parent { // same sort of deal with new List<SomeOtherType>()}

Upvotes: 1

Views: 542

Answers (1)

Rufus L
Rufus L

Reputation: 37050

If you promote the type T to the class, then it can be used by the class members:

public abstract class Parent<T>
{
    protected List<T> ListOfSomeType = new List<T>();

    protected void RemoveThing(T thing)
    {
        ListOfSomeType.Remove(thing);
    }

    protected void AddThing(T thing)
    {
        ListOfSomeType.Add(thing);
    }

    protected void SwapThings(int index1, int index2)
    {
        var temp = ListOfSomeType[index1];
        ListOfSomeType[index1] = ListOfSomeType[index2];
        ListOfSomeType[index2] = temp;
    }
}

Then when creating Child, you specify the SomeType type when you define the Parent that it derives from:

public class Child : Parent<SomeType>
{
    public Child()
    {
        ListOfSomeType = new List<SomeType>();
    }
}

Upvotes: 3

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