c#4.0新特性之一: Dynamic Lookup (1)

Code
1

class Program
2

{
3

static void Main(string[] args)
4

{
5

dynamic foo1 = new Foo();
6

foo1.Do1();
7

foo1.Do2();
8

foo1.KissFanweixiao();
9

}
10

}
11

public class Foo
13

{
14

public void Do1()

{ Console.WriteLine("fanweixiao calls do1"); }
15

public void Do2()

{ Console.WriteLine("fanweixiao calls do2"); }
16

}

这段代码在vs2010中可以编译通过。但是在运行的时候会报错。这是必然，KissFanweixiao()这个方法无中生有嘛。

这里注意到这是个RuntimeBinderException，而内容是不能找到KissFanweixiao的符号。

dynamic这个关键字看起来跟3.0增加的var很像，但是从IL的角度上来看，就是天壤之别了，毕竟var是编译时就能确定的东西，而dynamic追求的就是在运行时再决定究竟是个什么东西。我们还是先注释掉foo1.KissFanweixiao();这一句，使程序可以正常运行，然后看ILDASM的结果：

o__SiteContainer0类，这个类下的<>p__Site1...和<>p__Site2...对应着Do1()和Do2()两个方法的Invoke。再细看此时的Main函数：

Code
.method private hidebysig static void Main(string[] args) cil managed
{
.entrypoint
// Code size 139 (0x8b)
.maxstack 7
.locals init ([0] object foo1)
IL_0000: newobj instance void LearnCSharp4.Foo::.ctor()
IL_0005: stloc.0
IL_0006: ldsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site1'
IL_000b: brtrue.s IL_0033
IL_000d: call class [System.Core]Microsoft.CSharp.RuntimeBinder.RuntimeBinder [System.Core]Microsoft.CSharp.RuntimeBinder.RuntimeBinder::GetInstance()
IL_0012: ldc.i4.0
IL_0013: ldc.i4.0
IL_0014: ldstr "Do1"
IL_0019: ldtoken [mscorlib]System.Object
IL_001e: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
IL_0023: ldnull
IL_0024: newobj instance void [System.Core]Microsoft.CSharp.RuntimeBinder.CSharpCallPayload::.ctor(class [System.Core]Microsoft.CSharp.RuntimeBinder.RuntimeBinder,
bool,
bool,
string,
class [mscorlib]System.Type,
class [mscorlib]System.Type[])
IL_0029: call class [System.Core]System.Scripting.Actions.CallSite`1 class [System.Core]System.Scripting.Actions.CallSite`1>::Create(class [System.Core]System.Scripting.Actions.CallSiteBinder)
IL_002e: stsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site1'
IL_0033: ldsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site1'
IL_0038: ldfld !0 class [System.Core]System.Scripting.Actions.CallSite`1>::Target
IL_003d: ldsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site1'
IL_0042: ldloc.0
IL_0043: callvirt instance void class [System.Core]System.Action`2::Invoke(!0,
!1)
IL_0048: ldsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site2'
IL_004d: brtrue.s IL_0075
IL_004f: call class [System.Core]Microsoft.CSharp.RuntimeBinder.RuntimeBinder [System.Core]Microsoft.CSharp.RuntimeBinder.RuntimeBinder::GetInstance()
IL_0054: ldc.i4.0
IL_0055: ldc.i4.0
IL_0056: ldstr "Do2"
IL_005b: ldtoken [mscorlib]System.Object
IL_0060: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
IL_0065: ldnull
IL_0066: newobj instance void [System.Core]Microsoft.CSharp.RuntimeBinder.CSharpCallPayload::.ctor(class [System.Core]Microsoft.CSharp.RuntimeBinder.RuntimeBinder,
bool,
bool,
string,
class [mscorlib]System.Type,
class [mscorlib]System.Type[])
IL_006b: call class [System.Core]System.Scripting.Actions.CallSite`1 class [System.Core]System.Scripting.Actions.CallSite`1>::Create(class [System.Core]System.Scripting.Actions.CallSiteBinder)
IL_0070: stsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site2'
IL_0075: ldsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site2'
IL_007a: ldfld !0 class [System.Core]System.Scripting.Actions.CallSite`1>::Target
IL_007f: ldsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site2'
IL_0084: ldloc.0
IL_0085: callvirt instance void class [System.Core]System.Action`2::Invoke(!0,
!1)
IL_008a: ret
} // end of method Program::Main

如果是var或Foo的话直接这样就完事了：

Code
1 IL_0000: newobj instance void LearnCSharp4.Foo::.ctor()
2 IL_0005: stloc.0
3 IL_0006: ldloc.0
4 IL_0007: callvirt instance void LearnCSharp4.Foo::Do1()
5 IL_000c: ldloc.0
6 IL_000d: callvirt instance void LearnCSharp4.Foo::Do2()
7 IL_0012: ret

OK，看出不同来了。然后取消掉对foo.KissFanweixiao();的注释，再编译，再用ILDASM看，Do1()和KissFanWeixiao()的地位应该是一样的——因为dynamic与编译时无关嘛（好像是废话...但是这点很重要）。我们再看一眼有三个方法后的MSIL：

Code
1.method private hidebysig static void Main(string[] args) cil managed
2{
3 .entrypoint
4 // Code size 205 (0xcd)
5 .maxstack 7
6 .locals init ([0] object foo1)
7 IL_0000: newobj instance void LearnCSharp4.Foo::.ctor()
8 IL_0005: stloc.0
9 IL_0006: ldsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site1'
10

IL_000b: brtrue.s IL_0033
11

IL_000d: call class [System.Core]Microsoft.CSharp.RuntimeBinder.RuntimeBinder [System.Core]Microsoft.CSharp.RuntimeBinder.RuntimeBinder::GetInstance()
12

IL_0012: ldc.i4.0
13

IL_0013: ldc.i4.0
14

IL_0014: ldstr "Do1"
15

IL_0019: ldtoken [mscorlib]System.Object
16

IL_001e: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
17

IL_0023: ldnull
18

IL_0024: newobj instance void [System.Core]Microsoft.CSharp.RuntimeBinder.CSharpCallPayload::.ctor(class [System.Core]Microsoft.CSharp.RuntimeBinder.RuntimeBinder,
19

bool,
20

bool,
21

string,
22

class [mscorlib]System.Type,
23

class [mscorlib]System.Type[])
24

IL_0029: call class [System.Core]System.Scripting.Actions.CallSite`1 class [System.Core]System.Scripting.Actions.CallSite`1>::Create(class [System.Core]System.Scripting.Actions.CallSiteBinder)
25

IL_002e: stsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site1'
26

IL_0033: ldsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site1'
27

IL_0038: ldfld !0 class [System.Core]System.Scripting.Actions.CallSite`1>::Target
28

IL_003d: ldsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site1'
29

IL_0042: ldloc.0
30

IL_0043: callvirt instance void class [System.Core]System.Action`2::Invoke(!0,
31

!1)
32

IL_0048: ldsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site2'
33

IL_004d: brtrue.s IL_0075
34

IL_004f: call class [System.Core]Microsoft.CSharp.RuntimeBinder.RuntimeBinder [System.Core]Microsoft.CSharp.RuntimeBinder.RuntimeBinder::GetInstance()
35

IL_0054: ldc.i4.0
36

IL_0055: ldc.i4.0
37

IL_0056: ldstr "Do2"
38

IL_005b: ldtoken [mscorlib]System.Object
39

IL_0060: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
40

IL_0065: ldnull
41

IL_0066: newobj instance void [System.Core]Microsoft.CSharp.RuntimeBinder.CSharpCallPayload::.ctor(class [System.Core]Microsoft.CSharp.RuntimeBinder.RuntimeBinder,
42

bool,
43

bool,
44

string,
45

class [mscorlib]System.Type,
46

class [mscorlib]System.Type[])
47

IL_006b: call class [System.Core]System.Scripting.Actions.CallSite`1 class [System.Core]System.Scripting.Actions.CallSite`1>::Create(class [System.Core]System.Scripting.Actions.CallSiteBinder)
48

IL_0070: stsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site2'
49

IL_0075: ldsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site2'
50

IL_007a: ldfld !0 class [System.Core]System.Scripting.Actions.CallSite`1>::Target
51

IL_007f: ldsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site2'
52

IL_0084: ldloc.0
53

IL_0085: callvirt instance void class [System.Core]System.Action`2::Invoke(!0,
54

!1)
55

IL_008a: ldsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site3'
56

IL_008f: brtrue.s IL_00b7
57

IL_0091: call class [System.Core]Microsoft.CSharp.RuntimeBinder.RuntimeBinder [System.Core]Microsoft.CSharp.RuntimeBinder.RuntimeBinder::GetInstance()
58

IL_0096: ldc.i4.0
59

IL_0097: ldc.i4.0
60

IL_0098: ldstr "KissFanweixiao"
61

IL_009d: ldtoken [mscorlib]System.Object
62

IL_00a2: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
63

IL_00a7: ldnull
64

IL_00a8: newobj instance void [System.Core]Microsoft.CSharp.RuntimeBinder.CSharpCallPayload::.ctor(class [System.Core]Microsoft.CSharp.RuntimeBinder.RuntimeBinder,
65

bool,
66

bool,
67

string,
68

class [mscorlib]System.Type,
69

class [mscorlib]System.Type[])
70

IL_00ad: call class [System.Core]System.Scripting.Actions.CallSite`1 class [System.Core]System.Scripting.Actions.CallSite`1>::Create(class [System.Core]System.Scripting.Actions.CallSiteBinder)
71

IL_00b2: stsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site3'
72

IL_00b7: ldsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site3'
73

IL_00bc: ldfld !0 class [System.Core]System.Scripting.Actions.CallSite`1>::Target
74

IL_00c1: ldsfld class [System.Core]System.Scripting.Actions.CallSite`1> LearnCSharp4.Program/'

o__SiteContainer0'::'<>p__Site3'
75

IL_00c6: ldloc.0
76

IL_00c7: callvirt instance void class [System.Core]System.Action`2::Invoke(!0,
77

!1)
78

IL_00cc: ret
79

} // end of method Program::Main

如果不喜欢看MSIL的话可以这样看：

Code
1private static void Main(string[] args)
2{
3 object foo1 = new Foo();
4 if (

o__SiteContainer0.<>p__Site1 == null)
5

{
6

o__SiteContainer0.<>p__Site1 = CallSite>.Create(new CSharpCallPayload(Microsoft.CSharp.RuntimeBinder.RuntimeBinder.GetInstance(), false, false, "Do1", typeof(object), null));
7

}
8

o__SiteContainer0.<>p__Site1.Target(

o__SiteContainer0.<>p__Site1, foo1);
9

if (

o__SiteContainer0.<>p__Site2 == null)
10

{
11

o__SiteContainer0.<>p__Site2 = CallSite>.Create(new CSharpCallPayload(Microsoft.CSharp.RuntimeBinder.RuntimeBinder.GetInstance(), false, false, "Do2", typeof(object), null));
12

}
13

o__SiteContainer0.<>p__Site2.Target(

o__SiteContainer0.<>p__Site2, foo1);
14

if (

o__SiteContainer0.<>p__Site3 == null)
15

{
16

o__SiteContainer0.<>p__Site3 = CallSite>.Create(new CSharpCallPayload(Microsoft.CSharp.RuntimeBinder.RuntimeBinder.GetInstance(), false, false, "KissFanweixiao", typeof(object), null));
17

}
18

o__SiteContainer0.<>p__Site3.Target(

o__SiteContainer0.<>p__Site3, foo1);
19

}

本文旨在为不方便下载和使用vs2010虚拟机朋友帮个忙.

(在后台编辑的时候报stack overflow的问题...无法提交...)