C# 0 The Complete Reference

obj

 (which is of type 

T

) is assigned the value 

null

. This assignment is valid only for 

reference types. As a general rule, you cannot assign 

null

 to a value type. (The exception to 

this rule is the 

nullable type,

 which is a special structure type that encapsulates a value type 

and allows the value 

null

. See Chapter 20 for details.) Therefore, without the constraint, the 

www.freepdf-books.com

---

PART I

C h a p t e r   1 8 :  

G e n e r i c s  

519

PART IPART I

assignment would not have been valid and the compile would have failed. This is one case 

in which the difference between value types and reference types might be important to a 

generic routine.

The value type constraint is the complement of the reference type constraint. It simply 

ensures that any type argument is a value type, including a