调用与创建类不同的泛型类型的构造函数

Question

我有这个问题，我希望这是一个简单的解决方案。我有以下课程（摘录），我想避免必须制作 public myImage(myImageimage), public myImage(myImageimage)、public myImage(myImageimage) 以及可能的其他变体（如 bool）。

class myImage<T> where T : struct
{
    private int width;
    private int height;
    private T[] img;

    // constructor: allocate new image
    public myImage(int Width, int Height)
    {
        img = new T[Width*Height];
        width = Width;
        height = Height;
    }

    public myImage(myImage<byte> image)
    {
        // allocate space for new
        width = image.Width;
        height = image.Height;
        img = new T[width * height];

        if (typeof(T) == typeof(byte))
        {
            // in and out = same type? use block copy
            Buffer.BlockCopy(image.Image, 0, img, 0, width * height * Marshal.SizeOf(typeof(T)));
        }
        else
        {
            // else copy image element by element
            for (int counter = 0; counter < width * height; counter++)
                img[counter] = (T)Convert.ChangeType(image[counter], typeof(T));
        }
    }

    public int Width
    { 
        get { return width; } 
    }

    public int Height
    {
        get { return height; }
    }

    public T[] Image
    {
        get { return img; }
    }

    public Object this[int index]
    {
        get { return img[index]; }
        set { img[index] = (T)Convert.ChangeType(value, typeof(T)); }
    }
}

我会这样使用它：

myImage<byte> img = new myImage<byte>(100,200); // create byte image
myImage<double> img2 = new myImage<double>(img); // create double-img2 from byte-img
myImage<int> img3 = new myImage<int>(img2); // or int-img3 from double-img2

那么，我是否必须为 byte、int、float、double 创建方法，还是可以用 1 个方法完成这一切？

Answer 1

您不能在构造函数中使用通用参数，但您可以像这样定义一个静态方法：

class myImage<T> where T : struct {

    public static myImage<T> FromImage<X>(myImage<X> image) where X : struct {
        // create the object and return it...
    }
}

然后像这样调用它

myImage<double> img2 = myImage<double>.FromImage<byte>(img);

Answer 2

您的构造函数不能从类本身获取额外的泛型类型，但您可以创建一些静态工厂方法，这些方法可以获取额外的类型：

class myImage<T> where T : struct
{
    // ...

    public static myImage<T> CreateFrom<TOther>(myImage<TOther> image) where TOther : struct
    {
        // allocate space for new
        width = image.Width;
        height = image.Height;
        img = new T[width * height];

        if (typeof(T) == typeof(byte))
        {
            // in and out = same type? use block copy
            Buffer.BlockCopy(image.Image, 0, img, 0, width * height * Marshal.SizeOf(typeof(T)));
        }
        else
        {
            // else copy image element by element
            for (int counter = 0; counter < width * height; counter++)
                img[counter] = (T)Convert.ChangeType(image[counter], typeof(T));
        }
    }
}

然后可以像这样调用：

myImage<double> img2 = myImage<double>.CreateFrom(img); // create double-img2 from byte-img
myImage<int> img3 = myImage<int>.CreateFrom(img2); // or int-img3 from double-img2