Question

Could someone please advise me if this is possible. I am looking at a code sample from Microsoft on GameState for their XNA framework. In one of the classes they use ‘Public ReadOnly’ array data members. Although not a practice that promotes OO but nothing wrong with that.

The class later instantiates it inside the constructor, so far so good, its documented on MSDN too.

PROBLEM: The class later iterates through the array in a class method and changes the data in the array. I looked on MSDN and Googled on it and everywhere I look it says flat out that will error out. Is there a special exception for read-only arrays?

Please advise.

public class InputState
{
    public readonly KeyboardState[] CurrentKeyboardStates;
    public readonly KeyboardState[] LastKeyboardStates;

    public InputState()
    {
        CurrentKeyboardStates = new KeyboardState[max];  
        LastKeyboardStates = new KeyboardState[max];  
    }
    //Does not make sense code...
    public void Update()
    {
        for (int i=0; i < max; ++i)
        {
            //this should throw errors...
            CurrentKeyboardStates[i] = LastKeyboardStates[i];  
            LastKeyboardStates[i] = Keyboard.GetState();
            //more code....
        }
    }
}

Answer 1

Changing elements of a read-only array is perfectly fine, you just cannot re-assign the reference. (cannot set CurrentKeyboardStates/LastKeyboardStates to a new array, etc.) The element values can be changed.