Why do use of unassigned Rect and Vector2 behave differently?

Visual Studio flags an error, "

Use of unassigned local variable 'r'

," at Line 11. But not at Line 7. Both

Vector2

and

Rect

are structs, not classes. Why am I allowed to assign a value to a member of an unassigned

Vector2

variable, but not to a member of an unassigned

Rect

variable?

Code (CSharp):

1. public class Clazz
2. {
3.     public void A()
4.     {
5.         Vector2 v;
6.  
7.         v.x = 1;
8.  
9.         Rect r;
10.  
11.         r.x = 1;
12.     }
13. }

 

Ah, because

x

is a field of

Vector2

, but it is a property of

Rect

.