C# implement class which behaves like 2dim array

Question

Is it possible to create custom collection, that would have initializing syntax like 2dim arrays, for example:

var matrix = new Matrix(){{1,1},{2,2}};

EDIT

I understand that it seems to looke like a very common question, but indexers is not a problem, problem is initializing syntax. This is my little whim. So, is it possible to get EXACTLY the same expression? The most simmilar I obtain is:

var matrix = new Matrix() { new List<int>() {1, 2} };

Answer 1

To achieve the implementation of the initialization syntax you can use collection initializers on your object but only if that object implements IEnumerable.

If the object implements IEnumerable then you can add an Add method that will be called when you initialize an object. As an example here is how you might initizlize entries in a simple matrix class:

public class Matrix : IEnumerable
{
    public int[,] _data = new int[3,3];

    public void Add(int x, int y, int value)
    {
        _data[x,y] = value;
    }
    public IEnumerator GetEnumerator()
    {
        throw new NotImplementedException();
    }    
}

I can initialize it like this:

var myObject = new Matrix() {
    {1,2,3}, 
    {0,0,10}
};

This will be the equivalent of writing:

var myObject = new Matrix();
myObject.Add(1,2,3);
myObject.Add(0,0,10);

Custom Collection Initializers is a question about custom collection initializers which, amongst other things, has a quote from the spec about them.

As mentioned earlier this only works for objects that implement IEnumerable. As demonstrated above you don't have to have a useful implementation of IEnumerable for this to work but I would discourage you from making something IEnumerable to get this behaviour if the object isn't really an IEnumerable.

Answer 2

public int this[int index1, int index2] { 
    // This is the get accessor. 
    get { 
        return index1 + index2;
    }
}

Source: http://www.java2s.com/Tutorial/CSharp/0140__Class/Atwodimensionalindexer.htm

Answer 3

If you want it to use the array initialize syntax just add an Add method and implement IEnumerable.

 public void Add(int a, int b) { ... }

Answer 4

You can emulate it, f.e. with an internal List:

To make it safe(ish) you would need to add lots of checks, to make it work via your Initializerlist you could provide and IEnumerable constructor and pass it into that.

AFAIK there is not a way to make your wish of "autodeconstructing" a Matrix true.

    // main method - declares a matrix, fills one value, prints all
    static void Main()
    {
        Mat m = new Mat(8, 8);
        m[4, 2] = 55;

        Console.WriteLine(m);
        Console.ReadLine();
    }

    private class Mat
    {
        public Mat(int mRow, int mCol)
        {
            maxCol = mCol;
            maxRow = mRow;
            // prefill data with 0 - could use default
            data = new List<int>(Enumerable.Range(0, mCol * mRow).Select(n => 0)); 
        }

        // https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/indexers/
        public int this[int row, int col]
        {
            get
            {
                return data[row * maxCol + col];
            }
            set { data[row * maxCol + col] = value; }
        }

        // lenghty to string method 
        public override string ToString()
        {
            var sb = new StringBuilder();
            sb.Append("[ ");
            for (int r = 0; r < maxRow; r++)
            {
                sb.Append("[ ");

                for (int c = 0; c < maxCol; c++)
                {
                    sb.Append(this[r, c]);
                    if (c < maxCol - 1)
                        sb.Append(", ");
                }
                sb.Append(" ]\n");
                if (r < maxRow - 1)
                    sb.Append(", ");
            }
            sb.Append(" ]\n");
            return sb.ToString();
        }

        private int maxCol;
        private int maxRow;
        private List<int> data { get; set; }
    }

Answer 5

class Matrix : IEnumerable
{
    List<int[]> rowList = new List<int[]>();

    public void Add(params int[] row)
    {
        rowList.Add(row);
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return rowList.GetEnumerator();
    }
}