indexes in c # work with memory

Question

I began to parse the topic indexers in c # and ran into a problem while running a test task:

Index.cs:

class Index
{
    double[] arr;
    public int Length
    {
        get;
        set;
    }
    public double this[int x]
    {
        get { return arr[x]; }
        set
        {
            arr[x] = value;
        }
    }
    public Index(double[] arr1, int x, int y)
    {    
        Length = y;    

        arr = arr1;

        for (int i = x; i <= y; i++)
        {
            if (i == 0)
            {
                arr[i] = arr1[i + 1];
            }
            else
            {
                arr[i - 1] = arr1[i];
            }
        }
    }
}

Program.cs

static void Main(string[] args)
{
    double[] array = { 1, 2, 3, 4 };        
    var indexer0 = new Index(array, 1, 2);
    Console.WriteLine(indexer0.Length);
    Console.WriteLine("Result = 2,3");       
    var indexer1 = new Index(array, 1, 2);
    Console.WriteLine(indexer1[0]);
    Console.WriteLine(indexer1[1]);
    Console.WriteLine("Copy 25");        
    var indexer2 = new Index(array, 1, 2);
    var indexer3 = new Index(array, 0, 2);
    indexer2[0] = 25;
    Console.WriteLine(indexer3[1]);
    Console.WriteLine("Array");
    foreach(var item in array)
    {
        Console.WriteLine(item);
    }

    Console.ReadKey();
}

As you can see after calling indexer1, I want the array values ​​to change to 2 and 3, and I get 3.3 (I understand that this is due to the fact that when I call indexer0 I change the values ​​to 2.3, I then work with array 2,3,3,4, I can fix this by writing the values ​​to a temporary variable, but then I can not copy the value from indexer2 to indexer3 (the required value is 25.) Please help me deal with two of these problems.

Answer 1

The problem with your implementation is that you are not making a copy of the original array. This creates a second reference to the same array

 arr = arr1;

so modifications inside the loop, like this one,

arr[i] = arr1[i + 1];

are moving around and overwriting elements of the original array.

Fix this by allocating a new array, and copying the content of the original one into it:

public int Length { get { return arr.Length; } }
public Index(double[] arr1, int x, int y) {
    arr = new double[y];
    Array.Copy(arr1, x, arr, 0, y);
}

Note that your Index will have a copy of the original array. If you want a "window" into the original array, not a copy (ie have changes to Main 's array be visible through index1 , index2 , etc. store arr unchanged, and also store the initial index in the private variable. You can now change the indexer implementation to do "index translation", ie subtracting the stored x from index to get the correct index:

class Index {
    private readonly double[] arr;
    private readonly int offset; // set this to x in the constructor
    public int Length { get { return arr.Length; } }
    public double this[int idx] {
        get { return arr[idx+offset]; }
        set { arr[idx+offset] = value; }
    }
    public Index(double[] arr1, int x, int y) {
        arr = arr1;
        offset = x;
    }
}

Demo.