C#3.0 为我们带来什么（3） —— 初始化器

对比代码
c#2.0
        Employee e1;
        private void ee1()
        {
            e1 = new Employee(1);
            e1.Age = 25;
            e1.Name = "james";
        }
c#3.0
        Employee 2;
        private void ee2()
        {
            e2 = new Employee(2) { Age = 25, Name = "james" };
        }
与自动属性一样，初始化器的c#3.0的最大特点就是语法简化。
来看下IL代码
c#2.0
.method private hidebysig instance void  ee1() cil managed
{
  // 代码大小       45 (0x2d)
  .maxstack  8
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  ldc.i4.1
  IL_0003:  newobj     instance void WindowsFormsApplication1.Employee::.ctor(int32)
  IL_0008:  stfld      class WindowsFormsApplication1.Employee WindowsFormsApplication1.TestInitializer::e1
  IL_000d:  ldarg.0
  IL_000e:  ldfld      class WindowsFormsApplication1.Employee WindowsFormsApplication1.TestInitializer::e1
  IL_0013:  ldc.i4.s   25
  IL_0015:  callvirt   instance void WindowsFormsApplication1.Employee::set_Age(int32)
  IL_001a:  nop
  IL_001b:  ldarg.0
  IL_001c:  ldfld      class WindowsFormsApplication1.Employee WindowsFormsApplication1.TestInitializer::e1
  IL_0021:  ldstr      "james"
  IL_0026:  callvirt   instance void WindowsFormsApplication1.Employee::set_Name(string)
  IL_002b:  nop
  IL_002c:  ret
} // end of method TestInitializer::ee1
c#3.0
.method private hidebysig instance void  ee2() cil managed
{
  // 代码大小       37 (0x25)
  .maxstack  3
  .locals init ([0] class WindowsFormsApplication1.Employee '<>g__initLocal0')
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  ldc.i4.2
  IL_0003:  newobj     instance void WindowsFormsApplication1.Employee::.ctor(int32)
  IL_0008:  stloc.0
  IL_0009:  ldloc.0
  IL_000a:  ldc.i4.s   25
  IL_000c:  callvirt   instance void WindowsFormsApplication1.Employee::set_Age(int32)
  IL_0011:  nop
  IL_0012:  ldloc.0
  IL_0013:  ldstr      "james"
  IL_0018:  callvirt   instance void WindowsFormsApplication1.Employee::set_Name(string)
  IL_001d:  nop
  IL_001e:  ldloc.0
  IL_001f:  stfld      class WindowsFormsApplication1.Employee WindowsFormsApplication1.TestInitializer::e2
  IL_0024:  ret
} // end of method TestInitializer::ee2
c#2.0中是这样来赋给age值的
  IL_0008:  stfld      class WindowsFormsApplication1.Employee WindowsFormsApplication1.TestInitializer::e1
（将参数压入堆栈）
  IL_000d:  ldarg.0
  IL_000e:  ldfld      class WindowsFormsApplication1.Employee WindowsFormsApplication1.TestInitializer::e1
  IL_0013:  ldc.i4.s   25
c#3.0是这样的
  IL_0008:  stloc.0（从堆栈中弹出到局部变量）
  IL_0009:  ldloc.0
  IL_000a:  ldc.i4.s   25
也就是e1的对象载入简化了。看代码大小也能发现新写法的优势。

对应的就是集合初始化
c# 2.0
            List<Employee> list1 = new List<Employee>();
            list1.Add(e1);
c# 3.0
            List<Employee> list2 = new List<Employee>
            {
                new Employee(3) { Age = 25, Name = "james" },
                new Employee(4) { Age = 26, Name = "tony" }
            };
对应的IL
c#2.0
.method public hidebysig instance void  dd() cil managed
{
  // 代码大小       21 (0x15)
  .maxstack  2
  .locals init ([0] class [mscorlib]System.Collections.Generic.List`1<class WindowsFormsApplication1.Employee> list1)
  IL_0000:  nop
  IL_0001:  newobj     instance void class [mscorlib]System.Collections.Generic.List`1<class WindowsFormsApplication1.Employee>::.ctor()
  IL_0006:  stloc.0
  IL_0007:  ldloc.0
  IL_0008:  ldarg.0
  IL_0009:  ldfld      class WindowsFormsApplication1.Employee WindowsFormsApplication1.TestInitializer::e1
  IL_000e:  callvirt   instance void class [mscorlib]System.Collections.Generic.List`1<class WindowsFormsApplication1.Employee>::Add(!0)
  IL_0013:  nop
  IL_0014:  ret
} // end of method TestInitializer::dd
c#3.0

.method public hidebysig instance void  newdd() cil managed
{
  // 代码大小       23 (0x17)
  .maxstack  2
  .locals init ([0] class [mscorlib]System.Collections.Generic.List`1<class WindowsFormsApplication1.Employee> list2,
           [1] class [mscorlib]System.Collections.Generic.List`1<class WindowsFormsApplication1.Employee> '<>g__initLocal1')
  IL_0000:  nop
  IL_0001:  newobj     instance void class [mscorlib]System.Collections.Generic.List`1<class WindowsFormsApplication1.Employee>::.ctor()
  IL_0006:  stloc.1
  IL_0007:  ldloc.1
  IL_0008:  ldarg.0
  IL_0009:  ldfld      class WindowsFormsApplication1.Employee WindowsFormsApplication1.TestInitializer::e1
  IL_000e:  callvirt   instance void class [mscorlib]System.Collections.Generic.List`1<class WindowsFormsApplication1.Employee>::Add(!0)
  IL_0013:  nop
  IL_0014:  ldloc.1
  IL_0015:  stloc.0
  IL_0016:  ret
} // end of method TestInitializer::newdd
两个的init是不同的，至于为什么3.0里会由编译器init出来第二个参数我还不大明白，还请各位看客指点。难道还会真的倒退了？

看到这里大家也该明白如何写代码才是最好的了吧。