Array Array.Copy as Console.WriteLine Constructor interface ToString

Clone

For creating shallow copies, the C# Clone method and ICloneable interface are available, but using these features causes confusion.

Inconsistent meaning

Usually avoiding Clone() is a good plan—it is clearer just to copy fields when necessary, as with Array.Copy or assignment.

Example

This program uses Clone() on a string array. The Array type implements ICloneable and the Clone call results in a copied array.

Info When we change the cloned array, the original is unchanged. We use a cast to change the type of the object returned by Clone.

using System;

string[] array = { "a", "b", "c" };
string[] cloned = array.Clone() as string[];

Console.WriteLine(string.Join(",", array));
Console.WriteLine(string.Join(",", cloned));
Console.WriteLine();

// Change the first element in the cloned array.
cloned[0] = "?";

Console.WriteLine(string.Join(",", array));
Console.WriteLine(string.Join(",", cloned));a,b,c
a,b,c

a,b,c
?,b,c

Internals

In the implementation of Clone, the Array.Clone static method is called. And Array.Clone calls into MemberwiseClone. Remember that System.Array implements System.ICloneable.

IL_0022:  callvirt   instance object [mscorlib]System.Array::Clone()
IL_0001:  call       instance object System.Object::MemberwiseClone().method public hidebysig newslot abstract virtual
        instance object  Clone() cil managed
{
} // end of method ICloneable::Clone

`ICloneable`

The Rock class implements ICloneable, and defines the Clone() public method. This is probably not "good" code, but if Clone is wanted for some reason, it will work.

Next We create a new instance of the Rock class with its public constructor. We pass 3 arguments to it.

Finally We invoke the Clone method on the first Rock instance and cast its result. We call Console.WriteLine—this calls To String.

using System;

class Rock : ICloneable
{
    int _weight;
    bool _round;
    bool _mossy;

    public Rock(int weight, bool round, bool mossy)
    {
        this._weight = weight;
        this._round = round;
        this._mossy = mossy;
    }

    public object Clone()
    {
        return new Rock(this._weight, this._round, this._mossy);
    }

    public override string ToString()
    {
        return string.Format("weight = {0}, round = {1}, mossy = {2}",
            this._weight,
            this._round,
            this._mossy);
    }
}

class Program
{
    static void Main()
    {
        Rock rock1 = new Rock(10, true, false);
        Rock rock2 = rock1.Clone() as Rock;

        Console.WriteLine("1. {0}", rock1);
        Console.WriteLine("2. {0}", rock2);
    }
}1. weight = 10, round = True, mossy = False
2. weight = 10, round = True, mossy = False

Discussion

Clone has some problems—the main issue is the question of shallow and deep copies. ICloneable does not define which kind of cloning is done.

So The developers using Clone are left guessing. This works against the whole point of interfaces, which is to define contracts.

Summary

We explored Clone() and the ICloneable interface. It is difficult to use this interface correctly—using custom methods is clearer.