as的奇怪行为操作符

本文关键字：操作符 as | 更新日期: 2023-09-27 18:13:07

所以我有以下代码:

 /// <summary>
/// The 'Prototype' abstract class
/// </summary>
abstract class ColorPrototype
{
    public abstract ColorPrototype Clone();
}
/// <summary>
/// The 'ConcretePrototype' class
/// </summary>
class Color : ColorPrototype
{
    private int _red;
    private int _green;
    private int _blue;
    // Constructor
    public Color(int red, int green, int blue)
    {
        this._red = red;
        this._green = green;
        this._blue = blue;
    }
    // Create a shallow copy
    public override ColorPrototype Clone()
    {
        Console.WriteLine(
          "Cloning color RGB: {0,3},{1,3},{2,3}",
          _red, _green, _blue);
        return this.MemberwiseClone() as ColorPrototype;
    }
}
/// <summary>
/// Prototype manager
/// </summary>
class ColorManager
{
    private Dictionary<string, ColorPrototype> _colors =
      new Dictionary<string, ColorPrototype>();
    // Indexer
    public ColorPrototype this[string key]
    {
        get { return _colors[key]; }
        set { _colors.Add(key, value); }
    }
}
在main方法中我有: 
ColorManager colormanager = new ColorManager();
// Initialize with standard colors
colormanager["red"] = new Color(255, 0, 0);
// User clones selected colors
ColorPrototype p1 = colormanager["red"].Clone();
bool isColor = p1 is Prototype.Color;
Color color1 = p1 as Color;

我的问题是为什么变量p1具有类型Color (isColor是真的)，如果在克隆方法中我将结果转换为ColorPrototype (return this.MemberwiseClone() as ColorPrototype;) ?

参考:http://www.dofactory.com/net/prototype-design-pattern

as的奇怪行为操作符

this.MemberwiseClone()返回Color对象。所以p1实际上是Color。

如果向上转换为ColorPrototype则无关紧要。它的运行时类型仍然是Color。这相当于:

string s = "foo";
object o = s as object;
// runtime o type is still string

如果在clone方法中我将结果强制转换为ColorPrototype

因为即使您将p1强制转换为ColorPrototype, p1的运行时类型仍然是Color类型。强制转换引用类型允许您将类型T视为类型U，但它不会改变底层运行时类型。

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