C# copy 2D array (grid) with inherited unkown type

Question

Say we have a base class A which is abstract:

abstract class A {
  //code for class A
}

Also we have a subclass B which inherits from A and contains a copy constructor:

class B : A {

  //some other membervariables and methods  

  public B (B copy) {
    //makes a copy
  }
}

Now suppose we make a class GridObject which we want to inherit from A, and the grid elements it contains are also a type of A, but might be of type B or any other class that inherits from A:

class GridObject : A {
  A[,] grid;

  public GridObject (int columns, int rows) {
    grid = new A[columns, rows];
  }

  public GridObject (GridObject copy) {
    //makes a copy
  }

  public Add (A obj, int x, int y) {
    grid[x,y] = obj;
  }

Now, my problem is how to make a copy constructor that makes an exact copy of the GridObject. Suppose we do this:

B b = new B();
GridObject gridObject = new GridObject(5, 5);
for (int x = 0; x < 5; x++)
  for(int y = 0; y < 5; y++)
    gridObject.Add(new B (b), x, y);

Now, what is the best way to implement a (deep) copy constructor for the class GridObject? Note that the elements of our gridObject are of type B now. But this also might have been any other arbitrary class that inherits from A.

Daniel Becroft · Accepted Answer · 2011-11-10 21:03:43Z

2

Look at implementing System.IConeable[1] in A, and then overriding this for each of the inheriting classes. Each class can then be responsible for knowing how to clone itself.

[1] http://msdn.microsoft.com/en-us/library/system.icloneable.aspx

answered Nov 10, 2011 at 21:03

Daniel Becroft

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Community · Accepted Answer · 2017-05-23 11:55:50Z

0

For a generic deep copy helper method, see this SO question.

I'm not sure your classes should be responsible for making the copies though. Is there ever a chance a single object can be in two locations? Obviously I don't see the full implementation so I may be missing the use case, but I'd do something like this:

B b = new B();
GridObject gridObject = new GridObject(5, 5);
for (int x = 0; x < 5; x++)
  for(int y = 0; y < 5; y++)
    gridObject.Add(b.DeepClone(), x, y);

Note that I'm passing the copy into the constructor rather than relying on the constructor to make a copy for me.

edited May 23, 2017 at 11:55

CommunityBot

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answered Nov 10, 2011 at 21:09

Chris

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3 Comments

Quantum Over a year ago

I see the usefulness of the DeepCopy() method here. It should work instead of a copy constructor. But I don't understand exactly how to implement this method in the program. And what should be extended and marked as [Serializable]? Say I want to clone the gridObject: GridObject gridObjectCopy = gridObject.DeepCopy();

Chris Over a year ago

You'd add the Serializable attribute to your class. [Serializable]class GridObject : A {.... The linked question has a regular static method you can call and there's an extension method (used in my example). You can create a new static class ( called Utility for example) and paste that method into it. If you use the regular static version, you'd call it like Utility.DeepClone(gridObject). If you use the extension method, you'd call it like gridObject.DeepCopy().

Quantum Over a year ago

I see, this would be a good solution for custom made classes while not using some other framework.. In my case this I'm using XNA, so it would not work, because it can't make a deep copy for objects like Texture2D, because they are not marked as Serializable. I guess I should've mentioned that in the first place, sorry.

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