C# 0 The Complete Reference

Creating a Default Value of a Type Parameter

When writing generic code, there will be times when the difference between value types and 

reference types is an issue. One such situation occurs when you want to give a variable of a 

type parameter a default value. For reference types, the default value is 

null

. For non-

struct

value types, the default value is 0. The default value for a 

struct

 is an object of that 

struct

with all fields set to their defaults. Thus, trouble occurs if you want to give a variable of a 

type parameter a default value. What value would you use: 

null

, 0, or something else?

For example, given a generic class called 

Test

 declared like this:

class Test {

  T obj;

  // ...

if you want to give 

obj

 a default value, would you use

obj = null; // works only for reference types

or

obj = 0; // works only for numeric types and enums, but not structs

The solution to this problem is to use another form of 

default

, shown here:

default(

type

)

This is the operator form of 

default

, and it produces a default value of the specified 

type,

no

matter what type is used. Thus, continuing with the example, to assign