Question

Okay, I’ve this classes and main. I’m on VS 2010 Ultimate and .NET 4 Client.

internal class tezt
{
    private int[] _numeros = new int[5];
    public int[] Numeros
    {
        get { return _numeros; }
    }
}
public class tezt2
{
    private int[] _numeros = new int[5];
    public int[] Numeros
    {
        get { return _numeros; }
    }
}
class tezt3
{
    private int[] _numeros = new int[5];
    public int[] Numeros
    {
        get { return _numeros; }
    }
}
internal static class Program
{
    private static void Main()
    {
        var arrNums = new tezt();
        var arrNums2 = new tezt2();
        var arrNums3 = new tezt3();
        Console.WriteLine(arrNums.Numeros[0]);
        arrNums.Numeros[0] = 5;
        Console.WriteLine(arrNums.Numeros[0]);
        Console.WriteLine(arrNums2.Numeros[0]);
        arrNums2.Numeros[0] = 6;
        Console.WriteLine(arrNums2.Numeros[0]);
        Console.WriteLine(arrNums3.Numeros[0]);
        arrNums3.Numeros[0] = 7;
        Console.WriteLine(arrNums3.Numeros[0]);
        Console.ReadKey(true);
    }
}

What’s happening with these lines:

arrNums.Numeros[0] = 5;
arrNums2.Numeros[0] = 6;
arrNums3.Numeros[0] = 7;

Isn’t supposed that because the classes from which those objects are derived from haven’t a set parameter, those asignations must not be allowed?

What can be done to avoid that, to restrict that, thad doing thiks like arrNums.Numeros[0] = 5; throws a error?

Answer 1

You’re not setting the Numeros property, you are modifying an element at an index inside that property. You are only using the getter for that property.

The assignment that isn’t allowed is assigning a new value to that object’s property:

arrNums.Numeros = new int[5]; // will not compile.

You could make the getter return an IEnumerable<int> to protect it:

class tezt3
{
    private int[] _numeros = new int[5];
    public IEnumerable<int> Numeros
    {
        get { return _numeros; }
    }
}

You could also use a ReadOnlyCollection. The pros and cons of using IEnumerable<T> vs ReadOnlyCollection<T> are discussed in depth in this question.