Why Do Extension Methods Fail with Dynamic Objects in C#?

Extension Methods and the dynamic Keyword in C#

Using extension methods with dynamic objects in C# can lead to runtime errors. Let's illustrate this with an example:

<code class="language-csharp">List<int> list = new List<int>() { 5, 56, 2, 4, 63, 2 };
Console.WriteLine(list.First());</code>

This code works perfectly. However, if we try this:

<code class="language-csharp">dynamic dList = list;
Console.WriteLine(dList.First());</code>

A RuntimeBinderException is thrown. This happens because of how the compiler and runtime handle extension methods and dynamic objects.

Normally, the compiler searches for extension methods by examining all available static classes within the scope of the code, considering namespaces and using directives. This allows it to find the correct First() extension method from System.Linq.

With dynamic objects, the runtime doesn't have this compile-time information about namespaces and using directives. Including this information at runtime would be incredibly complex and inefficient. Therefore, the C# designers chose not to implement this functionality to avoid performance overhead and potential instability.

The above is the detailed content of Why Do Extension Methods Fail with Dynamic Objects in C#?. For more information, please follow other related articles on the PHP Chinese website!