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c#3.0系列Anonymous type in CLR3.5
我们说Anonymous Type是C# 3.0的新的特性，而没有说Anonymous Type是.NET Framework 3.5的新特性。这是因为Anonymous Type仅仅是.NET Programming Language和相应的Compiler的新引入的特征。而对于.NET Framework 3.5来说，它看不到这和原来有什么不同，对于Anonymous Type和一般的Named Type，对于CLR来说他们之间没有什么本质的区别。
通过下面这样的一段简单的代码：
1var p1 = new { Name = "IORI", Age = 27 };
然后我们再看看IL：
Code
1.method private hidebysig static void Main(string[] args) cil managed
2{
3 .entrypoint
4 // Code size 15 (0xf)
5 .maxstack 3
6 .locals init ([0] class '<>f__AnonymousType0`2'<string,int32> p1)
7 IL_0000: nop
8 IL_0001: ldstr "IORI"
9 IL_0006: ldc.i4.s 27
10 IL_0008: newobj instance void class '<>f__AnonymousType0`2'<string,int32>::.ctor(!0,
11 !1)
12 IL_000d: stloc.0
13 IL_000e: ret
14} // end of method Program::Main
15
我们再这里就可以看出Compiler将会为p1这个Anonymous Type创建一个名为<>f__AnonymousType0`2<string,int32>的类型。参数将根据数据成员的具体结构，这里也是声明一个类型。这个类继承自object，并且重写了ToString() 和 GetHashCode()的实现。所有的匿名类型自动继承自System.Object ，并且重写了Equals(), GetHashCode(), and ToString(). 如下图：
结构如下：
internal sealed class <>f__AnonymousType0<<Name>j__TPar, <Age>j__TPar>
{
// Fields
private readonly <Age>j__TPar <Age>i__Field;
private readonly <Name>j__TPar <Name>i__Field;
// Methods
public <>f__AnonymousType0(<Name>j__TPar Name, <Age>j__TPar Age);
public override bool Equals(object value);
public override int GetHashCode();
public override string ToString();
// Properties
public <Age>j__TPar Age { get; }
public <Name>j__TPar Name { get; }
}
再看看下面的例子。
Code
1class Program
2 {
3 static void Main(string[] args)
4 {
5 var p1 = new { Name = "IORI", Age = 27 };
6 var p2 = new { Name = "IORI", Age = 27 };
7 var p3 = new { Name = "GUOJUN", Age = 27 };
8 var p4 = new person { Name = "GUOJUN", Age = 27 };
9 Console.WriteLine("Base class of {0} is {1}", p1.GetType().Name, p1.GetType().BaseType);
10 Console.WriteLine("p1.ToString() = {0}", p1.ToString());
11 Console.WriteLine("p1.GetType() = {0}", p1.GetType());
12 Console.WriteLine("p3.GetType() = {0}", p3.GetType());
13 Console.WriteLine("p4.GetType() = {0}", p4.GetType());
14 Console.WriteLine("p1.GetHashCode() = {0}", p1.GetHashCode());
15 Console.WriteLine("(p1.GetHashCode() == p2.GetHashCode())= {0}", p1.GetHashCode() == p2.GetHashCode());
16 Console.WriteLine("(p1.GetHashCode() == p3.GetHashCode())= {0}", p1.GetHashCode() == p3.GetHashCode());
17 Console.WriteLine("p1.Equals(p2)= {0}", p1.Equals(p2));
18 Console.WriteLine("p1.Equals(p3)= {0}", p1.Equals(p3));
19 Console.WriteLine("p3.Equals(p4)= {0}", p3.Equals(p4));
20 Console.WriteLine("(p1 == p2)= {0}", p1 == p2);
21 Console.WriteLine("object.ReferenceEquals(p1.GetType(),p2.GetType()) = {0}", object.ReferenceEquals(p1.GetType(), p2.GetType()));
22 Console.WriteLine("object.ReferenceEquals(p1.GetType(),p3.GetType()) = {0}", object.ReferenceEquals(p1.GetType(), p3.GetType()));
23 Console.WriteLine("object.ReferenceEquals(p3.GetType(),p4.GetType()) = {0}", object.ReferenceEquals(p3.GetType(), p4.GetType()));
24 Console.Read();
25 }
26 }
27
28 class person
29 {
30 public int Age {get;set;}
31 public string Name {get; set;}
32 }
33
我们看看输出的结果。
通过以上的结果我们更能对Compiler会为Anonymous Type创建的类型更好的理解。
GetHashCode() 实现时，根据匿名类型的每个成员作为System.Collections.Generic.EqualityComparer<T>的输入，来计算hash值。因此，如果2个匿名类型有相同的属性字段，同时每个字段的值也相同，那么生成的Hash值也就相等。
ToString() 只是简单的用 属性名称/属性值 构造了一个字符串。
Equals() 结果相等，因为它使用值来比较相等。
== 结果不等，因为匿名类型没有重载 == 和 != , 这两个操作符默认情况下，比较的是对象的引用而不是值。
总结：
• Anonymous types继承 System.Object.
• The fields and properties 是read-only.
• Anonymous types 不支持events, custom methods, custom operators, or custom overrides.
• Anonymous types 是个密封类.
• Anonymous types 用自己定义的构造方法（不可以修改）来创建的.
最重要的是
Compiler在生成Anonymous types 的时候，并不是为每个如{N=?, N2 =? , ...}的结构生成一个不同的Type，它只会为不同的参数列表的结构：参数的名称，参数的数据类型，参数的相互顺序定义不同的Type(不包含参数的值)。而具有相同的参数列表的{N=?, N2 =? , ...}会共享同一个Type。但是这种仅限于在同一个Assembly中，编译器只会生成一个匿名类型，这些对象都是该唯一的匿名类型的实例。
结构如下：
internal sealed class <>f__AnonymousType0<<Name>j__TPar, <Age>j__TPar>
{
// Fields
private readonly <Age>j__TPar <Age>i__Field;
private readonly <Name>j__TPar <Name>i__Field;
// Methods
public <>f__AnonymousType0(<Name>j__TPar Name, <Age>j__TPar Age);
public override bool Equals(object value);
public override int GetHashCode();
public override string ToString();
// Properties
public <Age>j__TPar Age { get; }
public <Name>j__TPar Name { get; }
}
再看看下面的例子。
Code
1class Program
2 {
3 static void Main(string[] args)
4 {
5 var p1 = new { Name = "IORI", Age = 27 };
6 var p2 = new { Name = "IORI", Age = 27 };
7 var p3 = new { Name = "GUOJUN", Age = 27 };
8 var p4 = new person { Name = "GUOJUN", Age = 27 };
9 Console.WriteLine("Base class of {0} is {1}", p1.GetType().Name, p1.GetType().BaseType);
10 Console.WriteLine("p1.ToString() = {0}", p1.ToString());
11 Console.WriteLine("p1.GetType() = {0}", p1.GetType());
12 Console.WriteLine("p3.GetType() = {0}", p3.GetType());
13 Console.WriteLine("p4.GetType() = {0}", p4.GetType());
14 Console.WriteLine("p1.GetHashCode() = {0}", p1.GetHashCode());
15 Console.WriteLine("(p1.GetHashCode() == p2.GetHashCode())= {0}", p1.GetHashCode() == p2.GetHashCode());
16 Console.WriteLine("(p1.GetHashCode() == p3.GetHashCode())= {0}", p1.GetHashCode() == p3.GetHashCode());
17 Console.WriteLine("p1.Equals(p2)= {0}", p1.Equals(p2));
18 Console.WriteLine("p1.Equals(p3)= {0}", p1.Equals(p3));
19 Console.WriteLine("p3.Equals(p4)= {0}", p3.Equals(p4));
20 Console.WriteLine("(p1 == p2)= {0}", p1 == p2);
21 Console.WriteLine("object.ReferenceEquals(p1.GetType(),p2.GetType()) = {0}", object.ReferenceEquals(p1.GetType(), p2.GetType()));
22 Console.WriteLine("object.ReferenceEquals(p1.GetType(),p3.GetType()) = {0}", object.ReferenceEquals(p1.GetType(), p3.GetType()));
23 Console.WriteLine("object.ReferenceEquals(p3.GetType(),p4.GetType()) = {0}", object.ReferenceEquals(p3.GetType(), p4.GetType()));
24 Console.Read();
25 }
26 }
27
28 class person
29 {
30 public int Age {get;set;}
31 public string Name {get; set;}
32 }
33
