CODEWITHSUNDEEP
c#classgenericsproperties
u17
u17

Reputation: 2824

Have property be the same type as property of another class

Can I have property StudentId of class StudentRegistered be the same type as Student.Id (i.e., byte) without mentioning byte in the StudentRegistered declaration?

I would like to define the Id type for each derived class of Person only once in my application. What am I missing?

public class Person<T>
{
    public T Id { get; set; }
    public string Name { get; set; }
}

public class Student : Person<byte> { }
public class Adult : Person<short> { }

public class StudentRegistered
{
    public /* type */ StudentId { get; set; }
    public int EventId { get; set; }
}

Edit, to clarify:

Upvotes: 0

Views: 133

Answers (3)

John Alexiou
John Alexiou

Reputation: 29244

No there is no way to do what you are asking because StudentRegistered will be two different types, one with byte for StudentId and one with short for StudentId.

There are serious design issues here by requiring different types for a common ID. Your best choise to have common base interface with a InnerID method and then link the interfface with the registration. 

public interface IPerson
{
    ValueType InnerID { get; }
}

public abstract class Person<T> : IPerson
    where T : struct
{
    public T ID { get; set; }
    protected abstract ValueType InnerID { get; }
    ValueType IPerson.InnerID { get { return InnerID; } }
}
public class Student : Person<byte>
{
    protected override ValueType InnerID
    {
        get { return ID; }
    }
}
public class Adult : Person<short>
{
    protected override ValueType InnerID
    {
        get { return ID; }
    }
}

public class StudentRegistered
{
    public ValueType StudentID { get { return Person.InnerID; } }
    public IPerson Person { get; set; }
    public int EventId { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        var A=new Student() { ID=100 }; // byte
        var B=new Adult() { ID=1000 };  // short

        var regA=new StudentRegistered() { Person=A };
        Console.WriteLine("Type: {0} Value: {1}", regA.StudentID.GetType().Name, regA.StudentID);
        // Type: Byte Value: 100
        var regB=new StudentRegistered() { Person=B };
        Console.WriteLine("Type: {0} Value: {1}", regB.StudentID.GetType().Name, regB.StudentID);
        // Type: Int16 Value: 1000
    }
}

Upvotes: 1

Lee
Lee

Reputation: 144106

You'll have to use generics somewhere, you could do:

public class StudentRegistered<TS, TId> where TS : Person<TId>
{
  public TId StudentId {get; set;}
  public int EventId {get; set;}
}

Upvotes: 0

Selman Gen&#231;
Selman Gen&#231;

Reputation: 101680

Yes, you can make it generic and inherit from Person<T>

public class StudentRegistered<T> : Person<T>
{
   public T StudentId {get; set;};
   public int EventId {get; set;};
}

Upvotes: 1

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