Question

I deal with a framework on a daily basis where we sometimes provide methods that accept IEnumerable<MyBusinessObject> as a parameter in order to show user interfaces, perform calculations etc.

If I pass in an array of MyBusinessObject like so:

MyBusinessObject[] myArray = new MyBusinessObject { obj1, obj2, ..., objN };
frameworkClass.MyMethod(myArray);

....

public class FrameworkClass
{
    public void MyMethod(IEnumerable<MyBusinessObject> objs)
    {
        // Other code that uses the enumerable
        MyBusinessObject[] objectArray = objs.ToArray();            
        // More code that uses the enumerable
    }
}

Does the line objs.ToArray() simply resolve the IEnumerable<MyBusinessObject> back to the original array, or does it copy it to a whole new array, ready for use?

Answer 1

No, you will always get a new copy of the array, though the objects in it aren’t copies, they are the same references as in the original array.

It would be very inconsistent for changes to the returned array to sometimes affect the source and sometimes not. ToList works the same way for the same reason.

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You can check source code (as of 2015) if you need to review details: Enumerable.ToArray which in turn creates copy of elements (optimized for ICollection and hence Array[], but still making copy) with internal Buffer class.