CODEWITHSUNDEEP
c#inheritance
Daniel Mošmondor
Daniel Mošmondor

Reputation: 19956

Upcasting related - class conversion

I have a class, for example:

 class BaseDataPoint
 {
     public double A;
     public double B;
 }

and later on in the code, I need to extend that to

 class ReportDataPoint : BaseDataPoint
 {
     public double C;
 }

Since above is only an example, and there are lot more fields to copy, is it possible (via some trick) to 'convert' BaseDataPoint instance to ReportDataPoint without manually copying field by field?

If I have

 BaseDataPoint p1;
 ...
 ReportDataPoint p2=(ReportDataPoint)p1;  // FAILS at runtime
 ReportDataPoint p3=new ReportDataPoint(p1);  //  can't compile

Upvotes: 2

Views: 147

Answers (4)

Persi
Persi

Reputation: 345

It only depends on the type of the instance you create.

If you try :

BaseDataPoint p1 = new ReportDataPoint();

You will be able to cast it later.

otherwise you can implement a generic util class to transfer field values between instance types. once for all.

Upvotes: 0

rtpg
rtpg

Reputation: 2439

Just write a constructor inside ReportDataPoint, so that p3's initialisation will compile. It's work, but it'll enable you to define default values for the newer fields. class 

BaseDataPoint
    {
        public double A;
        public double B;
        public BaseDataPoint(double A, double B)
        {
            this.A = A;
            this.B = B;
        }
    }

    class ReportDataPoint : BaseDataPoint
     {
        static const double defaultCValue = 0.0;
        public double C;
        public ReportDataPoint(double A, double B, double C)
         :base(A,B){
            this.C = C;
          }

       public ReportDataPoint(BaseDataPoint p,double C=defaultCValue) :
        this(p.A, p.B, C)
       { }
    }

    ...
    BaseDataPoint p1=new BaseDataPoint(1,2);

    ReportDataPoint p2=new ReportDataPoint(p1);

Upvotes: 1

Marc Gravell
Marc Gravell

Reputation: 1062865

You can't change the type of an instance; you need to create a new instance. Furthermore, you can't use the cast syntax for this since you re not allowed to add custom operators within the inheritance chain.

So; either add a manual conversion (via adding a constructor like your example, or a ComvertTo method) - or there are a few libraries that may help (maybe AutoMapper, up it some serialization lins might help too).

Upvotes: 1

Florian Greinacher
Florian Greinacher

Reputation: 14784

Not that I know of. In cases like this I would just implement a constructor for ReportDataPoint that accepts a BaseDataPoint instance and copies the relevant data.

Upvotes: 0

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