C# 3.0 Cookbook, 3rd Edition

3.4. Indirectly Overloading the +=, -=, /=, and *= Operators

Problem

You need to control the handling of the +=, -=, /=, and *= operators within your data type; unfortunately, these operators cannot be directly overloaded.

Solution

Overload these operators indirectly by overloading the +, -, /, and * operators, as demonstrated in Example 3-5.

Example 3-5. Overloading the +, -, /, and * operators

public class Foo
{
    // Other class members...
    // Overloaded binary operators
    public static Foo operator +(Foo f1, Foo f2)
    {
       Foo result = new Foo( );
       // Add f1 and f2 here...
       // place result of the addition into the result variable.
       return result;
    }
    public static Foo operator +(int constant, Foo f1)
    {
       Foo result = new Foo( );
   // Add the constant integer and f1 here...
   // place result of the addition into the result variable.
   return result;
   }
   public static Foo operator +(Foo f1, int constant)
   {
      Foo result = new Foo( );
      // Add the constant integer and f1 here...
      // place result of the addition into the result variable.
      return result;
   }
      // The pattern above is repeated for the -, *, and . operators as well...
}

Discussion

While it is illegal to overload the +=, -=, /=, and *= operators directly, you can overload them indirectly by overloading the +, -, /, and * operators. The +=, -=, /=, and *= operators use the overloaded +, -, /, and * operators for their calculations.

The four operators +, -, /, and * are overloaded by the methods in the Solution section of this recipe. You might notice that each ...