What's the ideal dispatch mechanism?

Someone [asked] in r/golang: > I'm creating a multi-format converter that converts all graphic formats used on a user's > system to JPG. I can use a switch based on the file extension to choose how to convert > each file. Is there a more idiomatic way to structure the code, or is a switch preferable > for this kind of problem? What construct would be more optimal to maintain, extend, and > use long term, based on your experience, in place of a switch (number of formats up to > 20)? I took a [stab] at it there. Here's the longer version. --- A switch is fine as a starting point, and I'd start there. Once you hit 10-20 formats, it becomes a long, central piece of code that you keep touching every time a new format shows up. But I still wouldn't change anything if maintaining a bunch of case arms isn't actually causing problems. But sometimes I don't start with a switch and instead go straight to a map of functions. This removes the growing conditional. Adding a new format becomes a one-line map entry instead of editing a big block: This is usually where I stop. But you can keep going and replace the map of functions with a map of interfaces. Instead of a flat function map, you define a converter interface and keep a registry of types that satisfy it. The dispatch logic stays the same: Now instead of a map of functions, you keep a registry of converters: Each format can live in its own file and register itself. This avoids touching central code when adding new formats, which is the main long-term win: I rarely go for the interface approach unless I know for sure that the map of functions is a bottleneck, which almost never happens. It feels a bit heavy, and I'm not a big fan of the extra abstraction unless it actually solves a real problem. --- If you want to avoid global state in the map of func approach, wrap the map in a struct and hang Convert off of it: [asked]: https://www.reddit.com/r/golang/comments/1s8j4qj/ [stab]: https://www.reddit.com/r/golang/comments/1s8j4qj/comment/odh77wi/