C# 4.0 VS2010动态编程与新特性详解

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C# 4.0（Visual Studio 2010）是C#语言的一个重要升级，主要关注动态编程和与Visual Basic的协同进化。以下将详细介绍C# 4.0中的几个关键新功能： 1. **动态绑定（Dynamic Binding）**： C# 4.0引入了动态类型的概念，允许在运行时获取对象的属性和方法，而无需在编译时进行完全的类型检查。这使得处理来自动态语言（如Python或Ruby）的对象、通过IDispatch接口访问的COM对象、通过反射获取.NET类型以及结构可变的对象（如HTML DOM脚本对象）变得更加便捷。动态绑定提供了更大的灵活性，但同时也需要开发者在使用时更加谨慎，以确保程序的稳定性和性能。 2. **命名和可选参数（Named and Optional Arguments）**：新版本支持函数和方法的命名参数，允许调用者按照名称而非位置来传递参数，提高了代码的可读性和重用性。同时，C# 4.0还允许函数定义可选参数，即参数可以有默认值，这样在不提供特定值的情况下，函数也能正常工作。 3. **COM互操作增强（Features for COM Interop）**：为了更好地与COM组件交互，C# 4.0提供了改进的COM互操作特性，简化了调用过程，使得.NET框架内的C#代码能更自然地与COM对象集成。这包括自动装箱和拆箱、改进的异常处理以及更好的类型转换，提高了开发者的工作效率。 4. **泛型协变和逆变（Variance）**：泛型的协变和逆变是C# 4.0中的一个重要创新，它允许在某些情况下，泛型类型的参数可以是其基类型的超集或子集。这对于处理集合、委托和其他依赖于类型关系的场景具有重大意义，增强了代码的灵活性。 5. **与Visual Basic的关系**： C# 4.0和Visual Basic之间的关系更为紧密，两者共享了许多新特性，但又保持各自语言的独特风格。这意味着开发者可以在两个平台上享受到相似的功能，而无需担心语言间的断裂或不兼容性。这种协同进化旨在提高开发者的生产力，并促进.NET生态系统的整体繁荣。总结来说，C# 4.0在保持静态类型安全的同时，通过引入动态绑定、命名参数、优化的COM互操作以及泛型协变等新特性，显著提升了与动态环境和Visual Basic的兼容性。这些变化使C#成为一个更灵活且适应现代开发需求的工具，为开发者提供了更丰富的编程体验。

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The type dynamic can be thought of as a special version of the type object, which signals that the

object can be used dynamically. It is easy to opt in or out of dynamic behavior: any object can be

implicitly converted to dynamic, “suspending belief” until runtime. Conversely, expressions of type

dynamic can be implicitly converted to object, or indeed any other type, as long as there exists a

conversion at runtime:

dynamic d = 7; // compile-time implicit conversion

int i = d; // runtime implicit conversion

Dynamic operations

Not only method calls, but also field and property accesses, indexer and operator calls and even

delegate invocations and constructor calls can be dispatched dynamically:

dynamic d = GetDynamicObject(…);

d.M(7); // calling methods

d.f = d.P; // getting and settings fields and properties

d[“one”] = d[“two”]; // getting and setting through indexers

int i = d + 3; // calling operators

string s = d(5,7); // invoking as a delegate

var c = new C(d); // calling a constructor

The role of the C# compiler here is simply to package up the necessary information about “what is being

done to d”, so that the runtime can pick it up and determine what the exact meaning of it is given an

actual object d. Think of it as deferring part of the compiler’s job to runtime.

The result of any dynamic operation is itself of type dynamic, with two exceptions:

� The type of a dynamic constructor call is the constructed type

� The type of a dynamic implicit or explicit conversion is the target type of the conversion.

Runtime lookup

At runtime a dynamic operation is dispatched according to the nature of its target object d:

Dynamic objects

If d implements the interface IDynamicMetaObjectProvider, it is a so-called dynamic object, which

means that it will itself be asked to bind and perform the operation. Thus by implementing

IDynamicMetaObjectProvider a type can completely redefine the meaning of operations such as

method calls, member access etc. This is used intensively by dynamic languages such as IronPython and

IronRuby to implement their own dynamic object models. It is also used by APIs, e.g. by the Silverlight

HTML DOM to allow direct access to the object’s properties and methods using member access and

method call syntax instead of string-based accessor methods such as SetProperty or Invoke.

COM objects

If d is a COM object, the operation is dispatched dynamically through COM IDispatch. This allows

calling to COM types that don’t have a Primary Interop Assembly (PIA), and relying on COM features that

don’t have a counterpart in C#, such as default properties.

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