没有为“System.Int32”和“System.Double”类型定义二进制运算符“乘数”。 [英] The binary operator Multiply is not defined for the types 'System.Int32' and 'System.Double'.

问题描述

为什么以下代码在运行时抛出异常，而以传统的方式编译没有问题？

  var left = Expression.Constant（25d）; 
 var right = Expression.Constant（20）; 
 
 //抛出一个InvalidOperationException！ 
 var multiplyExpression = Expression.Multiply（left，right）; 
 
 var multiply = 25d * 20; 
 Debug.WriteLine（multiply.ToString（））; //正常工作
  

我不会使用 Expression.Convert 因为我无法确切地确定哪个表达式应该被转换。

解决方案

嗯，我想出了如何使用TypeCode解决问题枚举以确定哪个节点具有更高的类型精度，然后将后一个节点的类型转换为前者的类型，反之亦然：

  private static void访问（ref表达式left，ref表达式右）
 {
 var leftTypeCode = Type.GetTypeCode（left.Type）; 
 var rightTypeCode = Type.GetTypeCode（right.Type）; 
 
 if（leftTypeCode == rightTypeCode）
 return; 
 
 if（leftTypeCode> rightTypeCode）
 right = Expression.Convert（right，left.Type）; 
 else 
 left = Expression.Convert（left，right.Type）; 
} 
  

Why the following code throws an exception at runtime, whereas doing it in the traditional way compiles without problem?

var left = Expression.Constant(25d);
var right = Expression.Constant(20);

// Throws an InvalidOperationException!
var multiplyExpression = Expression.Multiply(left, right); 

var multiply = 25d * 20;
Debug.WriteLine(multiply.ToString()); // Works normally!

I won't use Expression.Convert since I can't determine exactly which expression should be converted.

解决方案

Well, I figured out how to solve the problem using TypeCode enumeration to determine which node would have higher type precision, then convert the latter node's type to the former's type, and vice versa:

  private static void Visit(ref Expression left, ref Expression right)
  {
     var leftTypeCode = Type.GetTypeCode(left.Type);
     var rightTypeCode = Type.GetTypeCode(right.Type);

     if (leftTypeCode == rightTypeCode)
         return;

     if (leftTypeCode > rightTypeCode)
        right = Expression.Convert(right, left.Type);
     else
        left = Expression.Convert(left, right.Type);
  }

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