关于C#的类型转换

【IT168技术文档】

  看下面的代码：

 //类型定义
    public interface I
{
string Name { get; set; }
}
public class A : I
{
public string Name { get; set; }
}
public class B : A
{
public int Key;
public static explicit operator string(B operand)
{
return operand.Name;
}
}
//方法调用
     private void button1_Click(object sender, EventArgs e)
{
B b = new B();
A a1, a2;
a1 = (A)b;
a2 = b as A;
string h = (string)b;
}
对应调用方法的IL代码：
.method private hidebysig instance void button1_Click(object sender, class [mscorlib]System.EventArgs e) cil managed
{
.maxstack 1
.locals init (
[0] class WindowsFormsApplication15.B b,
[1] class WindowsFormsApplication15.A a1,
[2] class WindowsFormsApplication15.A a2,
[3] string h)
L_0000: nop
L_0001: newobj instance void WindowsFormsApplication15.B::.ctor()
L_0006: stloc.0
L_0007: ldloc.0
L_0008: stloc.1
L_0009: ldloc.0
L_000a: stloc.2
L_000b: ldloc.0
L_000c: call string WindowsFormsApplication15.B::op_Explicit(class WindowsFormsApplication15.B)
L_0011: stloc.3
L_0012: ret
}

  这下很清楚了，()和as在做类型转换的时候都是一样处理的，根本不存在所谓那个性能好那个性能坏的问题，完全是受个人习惯影响的。