Generic C# Copy Constructor

Question

What would be the best way to write a generic copy constructor function for my c# classes? They all inherit from an abstract base class so I could use reflection to map the properties, but I'm wondering if there's a better way?

Answer 1

Avoid reflection if you can. Each class should have the responsibility of copying its own properties, and send it further to the base method.

Answer 2

A copy constructor basically means you have a single parameter, which is the object you're going to copy.

Also, do a deep copy, not a shallow copy.

If you don't know what deep and shallow copies are, then here's the deal:

Suppose you're copying a class that has a single row of integers as field.

A shallow copy would be:

public class Myclass()
{
    private int[] row;
    public MyClass(MyClass class)
    {
        this.row = class.row
    }
}

deep copy is:

public class Myclass()
{
    private int[] row;
    public MyClass(MyClass class)
    {
        for(int i = 0; i<class.row.Length;i++)
        {
            this.row[i] = class.row[i];
        }
    }
}

A deep copy really gets the actuall values and puts them in a new field of the new object, whilst a shallow copy only copies the pointers.

With the shallow copy, if you set:

row[3] = 5;

And then print both rows, both prints will have 5 as value of the 4th number. With a deep copy however, only the first print will have this, since the rows don't have the same pointers.

Answer 3

You can create a shallow copy efficiently with reflection by pre-compiling it, for example with Expression. For example, like so.

For deep copies, serialization is the most reliable approach.