在C＃中创建动态扩展方法？ [英] Creating a dynamic extension method in C#?

问题描述

是否可以解决此错误：

public static class LayoutExtensions
{
    /// <summary>
    /// Verifies if an object is DynamicNull or just has a null value.
    /// </summary>
    public static bool IsDynamicNull(this dynamic obj)
    {
        return (obj == null || obj is DynamicNull);
    }

编译时间

Error: The first parameter of an extension method 
       cannot be of type 'dynamic'  

$ b类型$ b

推荐答案

否。参见 https://stackoverflow.com/a/5311527/613130

使用 dynamic 对象时，无法通过扩展方法语法调用扩展方法。明确说明：

When you use a dynamic object, you can't call an extension method through the "extension method syntax". To make it clear:

int[] arr = new int[5];
int first1 = arr.First(); // extension method syntax, OK
int first2 = Enumerable.First(arr); // plain syntax, OK

这两个都可以，但是动态的

Both of these are ok, but with dynamic

dynamic arr = new int[5];
int first1 = arr.First(); // BOOM!
int first2 = Enumerable.First(arr); // plain syntax, OK

如果您知道 dynamic 对象起作用。 动态变量/字段/ ...只是对象变量/字段/ ...（加上属性），C＃编译器知道应该将其视为 dynamic 。 动态处理是什么意思？这意味着生成的代码而不是直接使用变量，而是使用反射在对象类型内搜索所需的方法/属性/ ...（因此，在这种情况下，在 int [] 类型）。显然，反射不能绕过所有已加载的程序集，以寻找可能在任何地方的扩展方法。

This is logical if you know how dynamic objects work. A dynamic variable/field/... is just an object variable/field/... (plus an attribute) that the C# compiler knows that should be treated as dynamic. And what does "treating as dynamic" means? It means that generated code, instead of using directly the variable, uses reflection to search for required methods/properties/... inside the type of the object (so in this case, inside the int[] type). Clearly reflection can't go around all the loaded assemblies to look for extension methods that could be anywhere.

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