C# 0 The Complete Reference

+

 is applied to two 

ThreeD

 objects, their coordinates are 

added together. When the 

+

 is applied to a 

ThreeD

 object and an integer, the coordinates 

are increased by the integer value.

While the overloading of 

+

 just shown certainly adds a useful capability to the 

ThreeD

class, it does not quite finish the job. Here is why. The 

operator+(ThreeD, int)

 method 

allows statements like this:

ob1 = ob2 + 10;

It does not, unfortunately, allow ones like this:

ob1 = 10 + ob2;

The reason is that the integer argument is the second argument, which is the right-hand 

operand, but the preceding statement puts the integer argument on the left. To allow both 

forms of statements, you will need to overload the 

+

 yet another time. This version must 

have its first parameter as type 

int

 and its second parameter as type 

ThreeD

. One version of 

the

operator+( )

 method handles 

ThreeD

 + integer, and the other handles integer + 

ThreeD

.

Overloading the 

+

 (or any other binary operator) this way allows a built-in type to occur on 

the left or right side of the operator. Here is a version 

ThreeD

 that overloads the 

+

 operator 

as just described:

// Overload the + for ThreeD + ThreeD, ThreeD + int, and int + ThreeD.

using System;

// A three-dimensional coordinate class.

class ThreeD {

  int x, y, z; // 3-D coordinates

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