Why Does Using `dynamic` with Extension Methods Throw an Exception?

Understanding the Interaction Between Extension Methods and dynamic

The provided code demonstrates a key difference in how the C# compiler and the Dynamic Language Runtime (DLR) handle extension methods.

A standard extension method call, like list.First(), works seamlessly because the compiler statically resolves the First() method at compile time. It searches through the known namespaces and using directives to find the correct extension method definition.

However, when using dynamic, as in dList.First(), the resolution is deferred until runtime by the DLR. The DLR lacks the ability to access the compiler's knowledge of namespaces and using directives at runtime. This limitation prevents the DLR from correctly locating the extension method, resulting in a runtime exception.

In essence, the compiler's static analysis provides the necessary information for resolving extension methods, while the DLR's runtime resolution lacks this crucial context. Therefore, directly using extension methods with dynamic objects is problematic.

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