如何防止在级联运算符中创建中间对象？

Question

我在我的应用程序中使用自定义Matrix类,我经常添加多个矩阵:

Matrix result = a + b + c + d; // a, b, c and d are also Matrices

但是,这为每个加法操作创建了一个中间矩阵.由于这是简单的添加,因此可以通过一次添加所有4个矩阵的元素来避免中间对象并创建结果.我怎么能做到这一点？

注:我知道我可以这样定义多种功能Add3Matrices(a, b, c),Add4Matrices(a, b, c, d)等,但我想保持的优美result = a + b + c + d.

Answer 1

您可以通过使用延迟评估将自己限制为单个小中间件.就像是

public class LazyMatrix
{
    public static implicit operator Matrix(LazyMatrix l)
    {
        Matrix m = new Matrix();
        foreach (Matrix x in l.Pending)
        {
            for (int i = 0; i < 2; ++i)
                for (int j = 0; j < 2; ++j)
                    m.Contents[i, j] += x.Contents[i, j];
        }

        return m;
    }

    public List<Matrix> Pending = new List<Matrix>();
}

public class Matrix
{
    public int[,] Contents = { { 0, 0 }, { 0, 0 } };

    public static LazyMatrix operator+(Matrix a, Matrix b)
    {
        LazyMatrix l = new LazyMatrix();
        l.Pending.Add(a);
        l.Pending.Add(b);
        return l;
    }

    public static LazyMatrix operator+(Matrix a, LazyMatrix b)
    {
        b.Pending.Add(a);
        return b;
    }
}

class Program
{
    static void Main(string[] args)
    {
        Matrix a = new Matrix();
        Matrix b = new Matrix();
        Matrix c = new Matrix();
        Matrix d = new Matrix();

        a.Contents[0, 0] = 1;
        b.Contents[1, 0] = 4;
        c.Contents[0, 1] = 9;
        d.Contents[1, 1] = 16;

        Matrix m = a + b + c + d;

        for (int i = 0; i < 2; ++i)
        {
            for (int j = 0; j < 2; ++j)
            {
                System.Console.Write(m.Contents[i, j]);
                System.Console.Write("  ");
            }
            System.Console.WriteLine();
        }

        System.Console.ReadLine();
    }
}