我也来说说Dynamic

看了很多人讨论Dynamic。不禁自己也想挖掘下。下面把自己的体会分享给大家

1.Dynamic关键字是为了方便访问某个对象。而跟DLR没太大关系。

使用了dynamic关键字创建的对象实际上是一个object. 使用.net 4.0以下的Reflector就可以看到.

使用dynamic关键字后编译器将会将这个对象后面的PropertyName翻译成相应Binder调用。因此语法检查器会忽略检查此对象是否包含PropertyName.

真正的跟DLR有关的是在System.Dynamic下的类型。

大家可以实验一个叫ExpandoObject的东西

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private static void Main(string[] args)
{
    dynamic expandoObject = new ExpandoObject(); expandoObject.
    PropertyA = "PropertyA";
    expandoObject.PropertyB = 2010;
    Console.WriteLine(expandoObject.PropertyA);
    Console.WriteLine(expandoObject.PropertyB);
}

这个时候用dynamic是不是有点动态语言的感觉了？所以说 dynamic不是DLR的实现，
但要用DLR在C#里最好的途径可能就是使用dynimic了。

2.Dynamic关键字是一个编译器做的语法糖

请看如下代码：

原始代码

<blockquote><pre class="brush: csharp; auto-links: true; collapse: false; first-line: 1; gutter: true; html-script: false; light: false; ruler: false; smart-tabs: true; tab-size: 4; toolbar: true;">public class Program
    {
        static void Main(string[] args)
        {
 
            Method1();
            Method2();
            Method3();
            Method4();
        }
 
 
        private static void Method1()
        {
            dynamic d = new TestClass();
            d.TestProperty = "";
        }
        private static void Method2()
        {
            TestClass t = new TestClass();
            dynamic d1 = t;
            dynamic d2 = t;
            d1.TestProperty = "";
            d2.TestProperty = "";
 
        }
        private static void Method3()
        {
            dynamic d = new TestClass();
            for (int i = 0; i < 100; i++)
            {
                d.TestProperty = i.ToString();
 
            }
        }
 
 
        private static void Method4()
        {
             
            for (int i = 0; i < 100; i++)
            {
                dynamic d = new TestClass();
                d.TestProperty = i.ToString();
 
            }
        }
 
   class TestClass
    {
        public string TestProperty { get; set; }
    }</pre></blockquote>public class Program
    {
        static void Main(string[] args)
        {
 
            Method1();
            Method2();
            Method3();
            Method4();
        }
 
 
        private static void Method1()
        {
            dynamic d = new TestClass();
            d.TestProperty = "";
        }
        private static void Method2()
        {
            TestClass t = new TestClass();
            dynamic d1 = t;
            dynamic d2 = t;
            d1.TestProperty = "";
            d2.TestProperty = "";
 
        }
        private static void Method3()
        {
            dynamic d = new TestClass();
            for (int i = 0; i < 100; i++)
            {
                d.TestProperty = i.ToString();
 
            }
        }
 
 
        private static void Method4()
        {
             
            for (int i = 0; i < 100; i++)
            {
                dynamic d = new TestClass();
                d.TestProperty = i.ToString();
 
            }
        }
 
   class TestClass
    {
        public string TestProperty { get; set; }
    }

用3.5语法反编译的
其实上面也都说的很清楚了编译器会把dynamic编译在一个和dynamic所在函数名有关的Static SiteContainer
如
<Method1>o__SiteContainer0
<Method2>o__SiteContainer2 …等

而且是一个dynamic生成一个Site .装在对应的Container中。

下面我们来看Method1 反编译后

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private static void Method1()
{
    object d = new TestClass();
    if (<Method1>o__SiteContainer0.<>p__Site1 == null)
    {
        <Method1>o__SiteContainer0.<>p__Site1 = CallSite<Func<CallSite, object, string, object>>.Create(Binder.SetMember(CSharpBinderFlags.None, "TestProperty", typeof(Program), new CSharpArgumentInfo[] { CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.None, null), CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.Constant | CSharpArgumentInfoFlags.UseCompileTimeType, null) }));
    }
    <Method1>o__SiteContainer0.<>p__Site1.Target(<Method1>o__SiteContainer0.<>p__Site1, d, "");
}

可以看出d其实是个Object了访问属性通过Site实现，而且这里的Site判空，意味着可以缓存。

Method2反编译后

private static void Method2()
{
    TestClass t = new TestClass();
    object d1 = t;
    object d2 = t;
    if (<Method2>o__SiteContainer2.<>p__Site3 == null)
    {
        <Method2>o__SiteContainer2.<>p__Site3 = CallSite<Func<CallSite, object, string, object>>.Create(Binder.SetMember(CSharpBinderFlags.None, "TestProperty", typeof(Program), new CSharpArgumentInfo[] { CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.None, null), CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.Constant | CSharpArgumentInfoFlags.UseCompileTimeType, null) }));
    }
    <Method2>o__SiteContainer2.<>p__Site3.Target(<Method2>o__SiteContainer2.<>p__Site3, d1, "");
    if (<Method2>o__SiteContainer2.<>p__Site4 == null)
    {
        <Method2>o__SiteContainer2.<>p__Site4 = CallSite<Func<CallSite, object, string, object>>.Create(Binder.SetMember(CSharpBinderFlags.None, "TestProperty", typeof(Program), new CSharpArgumentInfo[] { CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.None, null), CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.Constant | CSharpArgumentInfoFlags.UseCompileTimeType, null) }));
    }
    <Method2>o__SiteContainer2.<>p__Site4.Target(<Method2>o__SiteContainer2.<>p__Site4, d2, "");
}
 
虽然 d1 d2 都指向了 同一个对象t.但这里还是创建了两个Site。可见出现了多少个dynamic就会创建多少个site.<br><br>再看Method3和Method4

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private static void Method3()
    {
        object d = new TestClass();
        for (int i = 0; i < 100; i++)
        {
            if (<Method3>o__SiteContainer5.<>p__Site6 == null)
            {
                <Method3>o__SiteContainer5.<>p__Site6 = CallSite<Func<CallSite, object, string, object>>.Create(Binder.SetMember(CSharpBinderFlags.None, "TestProperty", typeof(Program), new CSharpArgumentInfo[] { CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.None, null), CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.UseCompileTimeType, null) }));
            }
            <Method3>o__SiteContainer5.<>p__Site6.Target(<Method3>o__SiteContainer5.<>p__Site6, d, i.ToString());
        }
    }

    private static void Method4()
    {
        for (int i = 0; i < 100; i++)
        {
            object d = new TestClass();
            if (<Method4>o__SiteContainer7.<>p__Site8 == null)
            {
                <Method4>o__SiteContainer7.<>p__Site8 = CallSite<Func<CallSite, object, string, object>>.Create(Binder.SetMember(CSharpBinderFlags.None, "TestProperty", typeof(Program), new CSharpArgumentInfo[] { CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.None, null), CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.UseCompileTimeType, null) }));
            }
            <Method4>o__SiteContainer7.<>p__Site8.Target(<Method4>o__SiteContainer7.<>p__Site8, d, i.ToString());
        }
    }