C# 0 The Complete Reference

int

, one for 

double

,

and one for objects of type 

ThreeD

. These are passed to the 

ByTwos

 constructor when 

objects of their respective types are created. Pay special attention to 

ThreeDPlusTwo( )

,

shown here:

// Define plus two for ThreeD.

static ThreeD ThreeDPlusTwo(ThreeD v) {

  if(v==null) return new ThreeD(0, 0, 0);

  else return new ThreeD(v.x + 2, v.y + 2, v.z + 2);

}

Notice that it first checks if 

v

 is 

null

. If it is, then it returns a new 

ThreeD

 object in which 

all fields are set to zero. The reason for this is that 

v

 is set to 

default(T)

 by the 

ByTwos

constructor. This value is zero for value types and 

null

 for object types. Thus, (unless 

SetStart( )

 has been called) for the first increment,