Hands-On Design Patterns and Best Practices with Julia

Using singleton types with dynamic dispatch

In Julia, function calls are dispatched according to the type of the arguments when the function is called. For a quick introduction to this mechanism, please refer to Chapter 3, Designing Functions and Interfaces.

Let's recall the use case that we presented earlier in this chapter about a command processor function. With a naive implementation, we have a large if-then-else block that dispatch to different functions according to the command string. Let's try to implement the same feature using singleton types.

For each command, we can define a function that takes a singleton type. For example, the signatures of the functions for the Open and Close events are as follows:

function process_command(::Val{:open}, ...