Autowire interface with one implementation

[sidux]

One feature that can reduce some boilerplate, is that we create automatically a service for each interface and point to the implementation automatically when there is only one.

For example :

class UserProvider(ABC)
class DatabaseUserProvider(UserProvider)

Don't have to write

container[UserProvider] = DatabaseUserProvider

What do you think ?

[GH-maggio]

Sounds like a great idea, any chance you have a rough idea how to implement this?

[meadsteve]

Whilst this is potentially a nice feature I'm hesitant on two fronts:

1. It's less explicit. There's now an implicit behaviour about what gets loaded. Currently in lagom all the loading is done explicitly so this is a fairly big change.

2. This may actually be surprisingly hard to implement in a thorough way. Python classes have a __subclasses__ property which would contain the "one implementation". However __subclasses__ only contains classes that have been loaded. So it's possible that a second subclass exists but it's not yet been loaded. This means that lagom would likely need to implement some directory scanning to find all possible classes.