Using array initializer

Question

I have a class called Matrix : IEnumerable<double>, (classic, mathematical matrix. It is basically a 2D array with some goodies).

The class is immutable, so there is no way to change its values after instance creation.

If want to create a matrix with pre-existing values I have to pass an array to the constructor like this:

double[,] arr = new double[,]
{
    {1,2,3}, {4,5,6}, {7,8,9}
};
Matrix m = new Matrix(arr);

Is there a way to turn it into this: (?)

Matrix m = new Matrix
{
    {1,2,3}, {4,5,6}, {7,8,9}
};

Update:

Found a hack-ish way yo make it work. I'm not sure if this solution is advisable, but it works.

class Matrix : ICloneable, IEnumerable<double>
{
        // Height & Width are initialized in a constructor beforehand.
        /*
         * Usage:
         * var mat = new Matrix(3, 4)
         * {
         *              {1,2,3}, {4,5,6}, {7,8,9}, {10,11,12}
         * };
         */
        int rowIndex;
        bool allowArrayInitializer;
        double[,] tempData;
        double[,] data;
        public void Add(params double[] args)
        {
                if(!allowArrayInitializer)
                        throw new InvalidOperationException("Cannot use array initializer");
                if(args.Length != Width || rowIndex >= Height)
                        throw new InvalidOperationException("Invalid array initializer.");
                for(int i = 0; i < Width; i++)
                        tempData[i, rowIndex] = args[i];
                if(++rowIndex == Height)
                        data = tempData;
        }
}

Of course you can do Matrix m = new Matrix(new double[,]{{1,2,3}, {4,5,6}, {7,8,9}}); — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Jul 7, 2013 at 16:13

Ry- · Accepted Answer · 2013-07-07 16:08:29Z

5

Not if it’s immutable; that syntactic sugar is implemented using Add().

answered Jul 7, 2013 at 16:08

Ry-♦

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10 Comments

Felix K. Over a year ago

With an interface? Would be nice to know, sometimes this is useful.

Gilad Naaman Over a year ago

Does the Add() method have to be public? I could live with it being mutable-if-you-don't-want-to-use-reflection.

Ry- Over a year ago

@FelixK.: I’m not sure, but I don’t think so. msdn.microsoft.com/en-us/library/vstudio/bb384062.aspx is all I’ve found so far…

Ry- Over a year ago

@FelixK.: It has to implement IEnumerable[<T>] but not IList or anything.

Ry- Over a year ago

@GiladNaaman: No, it’s not how vanilla arrays are implemented; arrays are a… more special feature of the language. They’ve also been around for much longer.

|

Karthik D V · Accepted Answer · 2013-07-07 16:56:26Z

0

You will not able to do it via initializer but should be able to do it via parameterized constructor. You can see the sample code below :

class Matrix : IEnumerable<double>
{
    double[,] input;
    public Matrix(double[,] inputArray)
    {
        input = inputArray;
    }

    public IEnumerator<double> GetEnumerator()
    {
        return (IEnumerator<double>)input.GetEnumerator();
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        return input.GetEnumerator();
    }
}

In the main method :

    static void Main(string[] args)
    {
        var m = new Matrix(new double[,] { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } });
    }

I hope this helps you!

answered Jul 7, 2013 at 16:56

Karthik D V

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3 Comments

Gilad Naaman Over a year ago

I don't see how it differs from the example I gave in the original post.

Ry- Over a year ago

This is… what the question wanted to avoid?

Karthik D V Over a year ago

@Gilad Naaman, I took around 15 mins to type, test and post. After posting I realized you have given the BEST answer !!!. Please do not simply reduce the points!

watfy · Accepted Answer · 2014-02-10 16:38:27Z

0

instead of deriving from IEnumerable I would use a property:

class Matrix 
{
        public double[,] Arr { get; set; }
}

Matrix m = new Matrix
{
      Arr = new double [,] { {1d,2d,3d}, { 4d,5d, 6d}}
};

answered Feb 10, 2014 at 16:38

watfy

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