Scala Cake Pattern and Dependency Collisions

Question

I\'m trying to implement dependency injection in Scala with the Cake Pattern, but am running into dependency collisions. Since I could not find a detailed example with such depe

Answer 1

"You're doing it wrong" (TM). You'd have the exact same problem with Spring, Guice or any IoC container: you're treating types as names (or symbols); you're saying "Give me an HTTP client" instead of "Give me an HTTP client suitable for communicating with fooApi".

In other words, you have multiple HTTP clients all named httpClient, which does not allow you to make any distinction between different instances. It's kind of like taking an @Autowired HttpClient without some way to qualify the reference (in Spring's case, usually by bean ID with external wiring).

In the cake pattern, one way to resolve this is to qualify that distinction with a different name: FooApiModule requires e.g. a def http10HttpClient: HttpClient and BarApiModule requires def connectionPooledHttpClient: HttpClient. When "filling in" the different modules, the different names both reference two different instances but are also indicative of the constraints the two modules place on their dependencies.

An alternative (workable albeit not as clean in my opinion) is to simply require a module-specific named dependency, i.e. def fooHttpClient: HttpClient, which simply forces an explicit external wiring on whomever mixes your module in.