Clean Code – How to Reduce a Switch in a Switch Statement

Your scenario doesn't sound like an appropriate use for an enumeration. Also, unless the values never change, this should be data driven.

If the values never change, then a key-value pair is more appropriate where the destination is the key and the flight number is the value. This would eliminate any need for a switch statement, as the key can be used to directly and efficiently locate the value.

if you really want to use an enum, then the switch statement in C# would be something like:

int flightNumber;
Destination selection = // some value collected from user input;

switch( selection )
{
    case Destination.London:
        flightNumber = 201;
    break;

    // etc.
}

This is a great fit for a map (2nd or 3rd proposed solution). I've used it dozens of times, and it's simple and effective. I don't really distinguish between these solutions; the important point is that there is a map with function names as the keys.

The major advantage of the map approach, in my opinion, is that the table is data. This means that it can be passed around, augmented, or otherwise modified at runtime; it's also easy to code additional functions which interpret the map in new, exciting ways. This wouldn't be possible with the case/switch solution.

I haven't really experienced the cons that you mention, but I would like to mention an additional drawback: dispatching is easy if only the string name matters, but if you need to take additional information into account in order to decide which function to execute, it's a lot less clean.

Perhaps I've just never run into a hard enough problem, but I see little value in both the command pattern and encoding the dispatch as a class hierarchy, as others have mentioned. The core of the problem is mapping requests to functions; a map is simple, obvious, and easy to test. A class hierarchy requires more code and design, increases the coupling between that code, and may force you to make more decisions upfront that you will later be likely to need to change. I don't think the command pattern applies at all.