Question

I am attempting to copy a number of arrays in c# using the Array.Copy() method. This method is supposed to automatically type-convert, however I am wondering if it will convert user-defined types if I were to define a constructor like so:

OldType(){
int param1;
String param2;
}

NewType(OldType old){
setParam1(old.param1);
setParam2(old.param2);
}

OldType oldArray[];
NewType newArray[];

//will this automatically convert???
Array.Copy(oldArray, newArray);

This is for use in converting from a legacy object to a new object. The content is exactly the same, the names are just different.

Answer 1

There’s an easy way to make this conversion without leaving yourself or anybody reading your code in doubt: use LINQ.

OldType[] oldArray = /* Some logic */;
NewType[] newArray = oldArray.Select(old => new NewType(old)).ToArray();

As the documentation here (pointed out by M.Babcock in the comments) says, Array.Copy is an O(n) operation. Likewise, the LINQ code I wrote above is an O(n) operation, so there is no asymptotic performance hit (actual performance in wall clock time is dependent on a host of factors, so I can’t compare the runtime of the two solutions without profiling) and you know that this code is correct.

Also from the MSDN docs:

If sourceArray and destinationArray are both reference-type arrays or are both arrays of type Object, a shallow copy is performed. A shallow copy of an Array is a new Array containing references to the same elements as the original Array. The elements themselves or anything referenced by the elements are not copied. In contrast, a deep copy of an Array copies the elements and everything directly or indirectly referenced by the elements.

So no, Array.Copy won’t “automatically convert” i.e. actually create new objects of type NewType during the copy, but will simply copy references to the objects of type OldType and put those references in newArray.