c# - C# 中的显式对象数组类型转换？

Question

如果我有两个类，并且在它们之间定义了显式类型转换，我是否不能将一个类的数组转换为另一个类的数组？

即。

using System;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Apple ted = new Apple() { Variety = Apple.EVariety.RedEllison };
            Orange bob = (Orange)ted; // explicit type conversion

            Apple[] apples = new Apple[] { ted };
            Orange[] oranges = new Orange[1];

            //oranges = apples; // why is this illegal ?

            // is this better ?
            oranges = Array.ConvertAll<Apple, Orange>(apples, new Converter<Apple, Orange>(p => (Orange)p));
        }

        class Apple
        {
            public enum EVariety { RedEllison, GrannySmith }
            public EVariety Variety;
        }

        class Orange
        {
            enum EColour { Unknown, Red, Green }
            EColour Colour;

            public static explicit operator Orange(Apple apple)
            {
                Orange result = new Orange();
                result.Colour = apple.Variety == Apple.EVariety.RedEllison ? result.Colour = EColour.Red : result.Colour = EColour.Green;
                return result;
            }
        }
    }
}

谢谢，罗斯

Answer 1

只有在源类型和目标类型之间存在引用转换时，转换才有效 - 换句话说，数组中的每个元素都可以用作任何一种类型，而无需更改数据。

来自 C# 规范，第 6.2.4 节(显式引用转换):

The explicit reference conversions are:

...

• From an array-type S with an element type SE to an array-type T with an element type TE, provided all of the following are true:
  • S and T differ only in element type. In other words, S and T have the same number of dimensions.
  • Both SE and TE are reference-types.
  • An explicit reference conversion exists from SE to TE.

在我看来，Array.ConvertAll 绝对是解决此问题的方法，但您应该能够使用类型推断使它变得更好:

oranges = Array.ConvertAll(apples, p => (Orange)p);