When Should You Avoid Using `dynamic` in C#?

Is it a Bad Practice to Use Dynamic?

Consider the following C# code:

MyClass myInstance        = new MyClass();
dynamic mydynamicInstance = myInstance;

//This method takes a MyClass argument and does something.
Caller.InvokeMethod(myDynamicInstance);

In this scenario, invoking a method with a dynamic argument allows for runtime type determination. While this may seem convenient, it harbors potential drawbacks.

Why Avoid Dynamic?

The dynamic keyword enables late type binding, meaning that the system checks type only during execution instead of compilation. This places the responsibility of error detection on the user, who may encounter unexpected exceptions or incorrect behavior.

Alternatives to Dynamic

Depending on the specific use case, there are several alternatives to using dynamic:

• Interface Virtual Call: Implement an interface with virtual methods and inherit it in derived classes.
• Extension Methods: Define extension methods to add specific functionality to existing types.
• Visitor Pattern: Create a visitor interface and visitor classes that interact with different types.
• Generic Method: Use a generic method that accepts parameters of various types.

Dynamic Alternatives for Unknown Method Calls

In cases where the method to be invoked is unknown at compile time, consider the following techniques:

• MethodInfo.CreateDelegate: Creates a delegate from a MethodInfo instance, providing a faster alternative to dynamic.
• DynamicMethod and ILGenerator.Emit: Allows for constructing a method from scratch, providing flexibility but requiring assembly knowledge.
• Linq Expression: Similar to DynamicMethod, but generates IL code without manual control.
• MethodInfo.Invoke: The standard reflection call, but slower than CreateDelegate.

Performance Considerations

Benchmarking results indicate that MethodInfo.CreateDelegate and DynamicMethod are relatively fast, while Keyword dynamic and MethodInfo.Invoke have significant performance overhead.

Conclusion

While dynamic may offer convenience, it sacrifices type safety and can lead to potential errors. In most cases, it is preferable to use alternative approaches that provide compile-time type checking and better performance. Dynamic should be used sparingly, such as in interoperability scenarios or when there is a clear advantage.

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