How to convert one object to another when both are different types but inherit from the same parent class

Question

I have 2 objects, Object A and Object B. A has the properties color and size and B has the the properties color, size and depth.

Both A and B inherits from C which is an abstract class.

How can I convert B to A at run-time?

 abstract class C {

 }

 Class A: C {
     int color;
     int size;
 }

 Class B: C {
     int color;
     int size;
     int depth;
 }

 main() {
     //creating object A
     A objA = new A();
     A.color = 46;
     A.size = 90;

     //creating object B
     B objB = new B();
     B.color = 23;
     B.size = 10;
     B.depth = 78;

     //How to do casting 
     A = B;
 }

Answer 1

You can add an explicit cast operator to the in class B :

Class B: C {
    int color;
    int size;
    int depth;
    public static explicit operator A(B b)
    {
        return new A() {color = b.color, size = b.size};
    }
}

You can then convert a B to an A using a cast:

A a = (A)b;

Answer 2

When I've had problems like this I've used AutoMapper.

This is a free library that will allow you to map one object to another and even allow you to map one field to another of a different name and type.

You can also convert a List<A> to List<B> which is handy.

AutoMapper Link on github

Edit

After reading your last comment I think AutoMapper might be your solution.

You do not explicitly need to specify anything other than;

AutoMapper.CreateMap<A,B>();

Then you can map;

B b = Mapper.Map<A,B>(sourceA);

Edit 2

Or use reflection yourself and create an extension that takes A as an argument and copies the appropriate fields / properties from A to B.

Answer 3

You can't directly convert B to A in this case without some extra work.

if you move the common fields into the base class then you can pass a B into a method that expects an instance of the base class and it will just access the common fields.

Your other options if you don't want to do that are to write a conversion method or add an implicit conversion so you can cast B to A or to use a library like Automapper as had been suggested

implicit conversion could look something like this

Public static implicit operator A (B theB)
{
    return new A (theB.colour, theB.size);
}

And would then allow you to cast your B instance to an A instance.

A myA = (A)myB;

I would still question if this is a good idea

Answer 4

It won't work like this. You are making two different variables with almost same attributes inside ?! Why so?

You can cast common fields into base class ! It is the best way here.