Using 'dynamic' in C# to implement Visitor Pattern

Question

I have an application where I am performing an operation on a series of elements and the exact nature of the operation depends on the type of the element being operated upon

Answer 1

Yes, I was considering this approach, but decided against it for a more traditional approach. I derive each visitor from an interface that has Visit methods for each type I want to implement the operation for.

If you have a number of different operations you want to implement as visitors, eg. Save and Load operations, and you might want to add more in the future; with the dynamic approach you don't get compilation errors if you forget to implement your operation for one of the types you need to handle. You'll only find out when the program crashes and burns at runtime.

I want to be sure at compile time that any operation has been implemented for all of the possible types.

Answer 2

Are there any gotchas with the dynamic dispatching that I haven't considered? I believe this is equivalent to performing a series of if (x is TypeA) Do((TypeA)x) else..., but I could be wrong.

The main gotcha would be if a type implements more than one interface in your visitor pattern - the compiler will probably pick the one you want, but it may not be the same choice you'd make if you use if (x is TypeA)/else if (x is TypeB) logic, as you'd control the order the checks occur.

Is this actually cleaner and easier to understand than a long if/elseif method?

I personally think so. This provides a very clean, fairly decently performing dispatch determined by the runtime type, and "just works." Hard to beat simple, short, clean code. Just make sure to (potentially) handle the case where you get a runtime error from the wrong type being passed in.