正常排版和使用__作为_关键字[重复]有什么区别?

as

object x = new object();
string y = x as string; // y == null
string z = (string)x; // InvalidCastException

http://blogs.msdn.com/b/ericlippert/archive/2009/10/08/what-s-the-difference-between-as-and-cast-operators.aspx

as

Object a = new Object();
String b = a as String;
if(b != null) // always false for this example.
{}

as null

((Class2) obj)  // Throws exception when the casting cannot be made

Class2 C = obj as Class2  //  Will return NULL if the casting cannot be made

null

public class A {}
public class B {}
...
A a = new A();
//B b = (B)a;  //compile error:Cannot implicitly convert type 'A' to 'B'

implicit explicit

as

expression as type

expression is type ? (type) expression : (type) null

expression

is

uint? u = 52;
int? i = (int?) u;   // 'i' is now 52

uint? u = 52;
object d = u;
int? i = d as int?;

uint? u = 52;
int? i = (u is int?) ? (int?) u : (int?) null;

“我现在” null

uint? u = 52;
int? i = u as int?;

哎呀。编译器错误。所以,我想这两种说法毕竟不完全相同。