为什么在使用动态参数链接方法时VS2010 IntelliSense失败 [英] Why VS2010 IntelliSense fails when chaining methods with dynamic args

问题描述

我想向您解释C＃4.0动态专家。

I would like some explanation of you experts in C# 4.0 dynamic.

我有一个熟练的生成器类，可以帮助在创建对象之前对其进行配置。该接口具有方法SetParameters（...）：

I have a fluent builder class to help configure an object before creating it. This interface has a method SetParameters(...):

    public FluentBuilder<TInterface> SetParameters(dynamic parameters)
    {
        _parameters = parameters;
        return this;
    }

我这样做是为了消耗流畅的界面：

I'm doing this to consume the fluent interface:

var order = new Order();

/* Setting up parameters */
dynamic parameters = new ExpandoObject();
parameters.Transaction = transactionObj;
parameters.CurrentPrincipal = Thread.CurrentPrincipal;

var proxiedOrder = ObjectProxyFactory
    .Configure<IOrder>(order)
    .FilterMethods(o => o.InsertOrder())
    .AddPreDecoration(AppConcerns.JoinSqlTransaction)
    .AddPreDecoration(AppConcerns.EnterLog)
    .AddPostDecoration(AppConcerns.ExitLog)
    .AddPostDecoration(AppConcerns.SecurityCheck)
    .SetParameters(parameters)
    .Teste() //this method doesn't exist in the fluent builder
    .CreateProxy();

var result = proxiedOrder.InsertOrder();

如上述代码段所述，流畅的接口中不存在称为Teste（）的方法，但是intelissense允许我在调用SetParameters之后像返回动态代码一样编写任何方法，但是正如您在代码中看到的那样，SetParameters返回的不是动态的FluentInterface。

As commented in the above snippet, the method called Teste() doesn't exists in the fluent interface, but intelissense allow write anymethod after I call SetParameters like it returning dynamic, but as you see in code, SetParameters returns FluentInterface that is not dynamic.

上面的代码已成功编译在运行时by将失败，因为在运行时将在FluentBuilder类中找不到Teste（）方法。

The code above compiles sucessfully by in runtime will fail because in runtime the method Teste() will not be found in FluentBuilder class.

在设计时解决此问题并获得正确的Intelissense ，我需要将参数转换为ExpandoObject类：

To resolve this problem in design-time, and to get correct Intelissense, I need to cast the parameter to the ExpandoObject class:

var proxiedOrder = ObjectProxyFactory
.Configure<IOrder>(order)
.FilterMethods(o => o.InsertOrder())
.AddPreDecoration(AppConcerns.JoinSqlTransaction)
.AddPreDecoration(AppConcerns.EnterLog)
.AddPostDecoration(AppConcerns.ExitLog)
.AddPostDecoration(AppConcerns.SecurityCheck)
.SetParameters((ExpandoObject)parameters) //cast to ExpandoObject
.Teste() //now intelissense is giving me an "red" error and solution will not compile
.CreateProxy();

var result = proxiedOrder.InsertOrder();

我发现，只要在任何方法链中传递C＃动态参数，该方法之后接收到动态参数后，对方法的后续调用将类似于返回C＃动态对象，即使该方法的返回类型不是动态的。

I've found that, anytime I pass a C# dynamic parameter in any method chaining, after that method receiving the dynamic parameter, the subsequent calls to methods will behave like returning a C# dynamic object, even if the return type of the method it's not dynamic.

这是一个错误？还是会发生这种情况？

Is it a bug ? Or is this expected to happens ?

推荐答案

会发生这种情况。任何涉及动态参数的方法调用都是动态解决的-确切的重载直到执行时才能确定，因此返回类型在编译时是未知的，因此将其视为 dynamic 。在某些情况下，C＃编译器可以推断出更多信息（例如，如果是静态方法调用），但为简单起见，它不能。只有很少一些涉及动态值的表达式具有非动态类型。 （从内存中， is 运算符始终为 bool ，并且始终假定构造函数返回正在构造的类型。 ）

It's expected to happen. Any method call involving a dynamic argument is resolved dynamically - the exact overload can't be determined until execution time, so the return type is unknown at compile time, so it's treated as being dynamic. In some cases the C# compiler could infer more information (e.g. if it's a static method call) but for simplicity it doesn't. Only a variable few expressions involving dynamic values have non-dynamic types. (From memory, the is operator is always bool, and a constructor is always assumed to return the type being constructed.)

编辑：我终于找到了规范参考。从第7.6.5节开始：

I've finally found the spec reference. From section 7.6.5:

如果至少有以下一项成立，则动态绑定调用表达式（第7.2.2节）：

An invocation-expression is dynamically bound (§7.2.2) if at least one of the following holds:

• 主表达式的编译时类型为动态。


• 可选参数列表的至少一个参数具有编译时

在这种情况下，编译器将invocation-expression分类为dynamic类型的值。

In this case the compiler classifies the invocation-expression as a value of type dynamic.

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