How can I instantitate a list based on the specific object type?

Question

I have the following definitions:

public class BaseEntity 
{
    ...
    public BaseEntity()
    {

    }
}

public class KeyValuePair
{
    public string key;
    public string value;
    public string meta;
}

public class KeyValuePairList : BaseEntity
{
    public List<KeyValuePair> List {set; get;}

    public KeyValuePairList(IEnumerable<KeyValuePair> list)
    {
        this.List = new List<KeyValuePair>();
        foreach (KeyValuePair k in list) {
            this.List.Add(k);
        }
    }
}

I have 10 more different classes like KeyValuePair and KeyValuePairList all achieving the same purpose - the former defines the object, the latter defines the list into which these objects should be placed. How can I incorporate this functionality into the base class BaseEntity so that I don't have to redefine the List instantiation logic in each individual class i.e. I want to be able to instantiate the list based on the object type being passed to the constructor? Any suggestions?

You have second BaseEntity class defined within the BaseEntity class? I don't think that's even possible. EDIT I think you meant that to be the constructor, right? — Kevin Aenmey
– Kevin Aenmey, Commented Jun 30, 2012 at 22:32
@Kevin: I assume that it's a typo, omit the class and you get a constructor. — Tim Schmelter
– Tim Schmelter, Commented Jun 30, 2012 at 22:34
@Kevin: Yes. Sorry! I was typing a simpler example looking at my IDE. Edited the question now. — Legend
– Legend, Commented Jun 30, 2012 at 22:35
How do your KeyValuePair classes differ? If they are all related in some way, could you not use a generic type parameter? — dash
– dash, Commented Jun 30, 2012 at 22:36

Kevin Aenmey · Accepted Answer · 2012-06-30 22:38:01Z

4

Can you use generics?

public class BaseEntity<T> where T: class
{
    public List<T> List { set; get; }

    public BaseEntity(IEnumerable<T> list)
    {
        this.List = new List<T>();
        foreach (T k in list)
        {
            this.List.Add(k);
        }
    }
}

public class KeyValuePair
{
    public string key;
    public string value;
    public string meta;
}

public class KeyValuePairList : BaseEntity<KeyValuePair>
{
    public KeyValuePairList(IEnumerable<KeyValuePair> list) 
        : base(list) { }
}

answered Jun 30, 2012 at 22:38

Kevin Aenmey

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1 Comment

Legend Over a year ago

+1 Awesome. Thank you. I was moving towards that approach after I found this: stackoverflow.com/questions/12051/… and now I have your answer as well. Thank you for your time.

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