Explanation about the clone the array containing cloneable objects is needed

Question

I am trying following code:

public class cloneTest : ICloneable {

    public string strValue { get; set; }

    public object Clone( ) {
      cloneTest n = new cloneTest( );
      n.strValue = this.strValue;
      return n;     
    }
}

cloneTest obj1 = new cloneTest( ) { strValue = "one" };
cloneTest obj2 = new cloneTest( ) { strValue = "two" };
cloneTest obj3 = new cloneTest( ) { strValue = "three" };

cloneTest[ ] strValueArray = new cloneTest[  ] {obj1, obj2, obj3};

cloneTest[ ] strValueArrayClone = ( cloneTest[ ] )strValueArray.Clone( );
strValueArrayClone[ 2 ].strValue = "four";

When I modify the strValuArrayClone object as specified in my code, this change also reflects in strValueArray object even though, I am creating clone. However if try below code, then everything work smoothly. I want to understand the logic behind it.

cloneTest obj1 = new cloneTest( ) { strValue = "one" };
cloneTest obj2 = new cloneTest( ) { strValue = "two" };
cloneTest obj3 = new cloneTest( ) { strValue = "three" };

cloneTest[ ] strValueArray = new cloneTest[  ] {obj1, obj2, obj3};

cloneTest[ ] strValueArrayClone = ( cloneTest[ ] )strValueArray.Clone( );
cloneTest obj2clone = ( cloneTest )obj2.Clone( );
obj2clone.strValue = "six";
strValueArrayClone[ 2 ] = obj2clone;

score 2 · Accepted Answer · answered May 28 '14 at 08:51

You are creating a clone of the array, but with the same contents. The array Clone() method is a shallow clone. Since the contents are references, the slots in both arrays refer to the same actual objects instances. In the first code sample, there are only 3 cloneTest instances no matter how many arrays you create with references to those 3 instances. If you change a property on one of those 3 objects, it will be visible everywhere that has a reference to that object - which means via every array.

Options:

create a deep clone (i.e. clone the internal items too, at the point of cloning the array)
clone objects at the point of changing properties (this is what your second code sample does)
- a special-case of this is to make the original types immutable, to preclude such occurrences

Thanks for explanation. I want to understand, what benefit, one can get with shallow clone? — User1551892, May 28 '14 at 08:59
@User1551892 it gives you an isolated snapshot of the array - before you start swapping references, etc. Note that for value-types, this will be a true clone of their internal values etc, but it is almost always (i.e. > 99% of the time) desirable to make structs immutable *anyway*. — Marc Gravell, May 28 '14 at 09:16

Explanation about the clone the array containing cloneable objects is needed

1 Answers1