* 运算符和类型转换器答案

【问题标题】：* operator and type converters* 运算符和类型转换器
【发布时间】：2015-03-22 13:42:41
【问题描述】：

我有以下。它按预期工作：

using System;
namespace Whatever {  
  public class DoubleWrapper {
    public double Payload { get; set; }
    public DoubleWrapper(double payload) {
      this.Payload = payload;
    }
    public static implicit operator DoubleWrapper(double x) {
      DoubleWrapper r = new DoubleWrapper(x);
      return r;
    }
    public static implicit operator double(DoubleWrapper wrapper) {
      double r = wrapper.Payload;
      return r;
    }
    public DoubleWrapper Times(DoubleWrapper multiplyByMe) {
      DoubleWrapper r = this * multiplyByMe;  // does compile
      return r;
    }
  }
}

但是，如果我将“double”替换为“Complex”，则会出现编译错误：

using System;
using System.Numerics;
namespace Whatever {
  public class ComplexWrapper {
    public Complex Payload { get; set; }
    public ComplexWrapper(Complex payload) {
      this.Payload = payload;
    }
    public static implicit operator ComplexWrapper(Complex x) {
      ComplexWrapper r = new ComplexWrapper(x);
      return r;
    }
    public static implicit operator Complex(ComplexWrapper wrapper) {
      Complex r = wrapper.Payload;
      return r;
    }
    public ComplexWrapper Times(ComplexWrapper multiplyByMe) {
      ComplexWrapper r = this * multiplyByMe; // ERROR: Operator '*' cannot be applied to operands of type Whatever.ComplexWrapper and Whatever.ComplexWrapper.
      return r;
    }

解决方法并不难——我可以像这样替换该行：

      ComplexWrapper r = this.Payload * multiplyByMe; //WORKS

我确实验证了 * 符号对 double 和 System.Numerics.Complex 都有效。确实如此：

namespace SomewhereElse { // different namespace
  public static class TestTimes {  // builds just fine
    public static void Products() {
      double x1 = 4;
      double x2 = 5;
      double product = x1 * x2;
      Complex z1 = new Complex(3, 4);
      Complex z2 = new Complex(3, -4);
      Complex zProduct = z1 * z2;
    }
  }
}

为什么构建了我的 DoubleWrapper 类，但没有构建我的 ComplexWrapper？

【问题讨论】：

标签： c# type-conversion operators

【解决方案1】：

在您的块 1 上，类型被隐式转换为 double，因此乘法有效，但在您的块 2 上没有乘法运算符。

如果您在第二堂课上添加以下代码，错误将消失。

    public static ComplexWrapper operator *(ComplexWrapper a, ComplexWrapper b)
    {
        var complex = a.Payload * b.Payload;
        return complex;
    }

编辑：精炼答案/第二种方法

编译器似乎将该类型提升为ComplexWrapper，这就是产生该错误的原因。

只需将this 转换为Complex，错误也会消失：

    public ComplexWrapper Times(ComplexWrapper multiplyByMe)
    {
        ComplexWrapper r = (Complex)this * multiplyByMe;
        // ERROR: Operator '*' cannot be applied to operands of type Whatever.ComplexWrapper and Whatever.ComplexWrapper.
        return r;
    }

【讨论】：