Nested Scopes

[valeriyo]

Is your feature request related to a problem? Please describe.
Currently, with Koin 2.0 it's possible to declare nested scopes:

module {
    scope(A) {
        scoped(NUMBER) { 123 }

        // nested scope!
        scope(B) {
            scoped(STRING) { get(NUMBER).toString() }
        }
    }
}

With implied understanding that:

1. An instance of scope B can be created from an instance of scope A (but not from the global Koin),
2. Scope B "sees" all bindings from scope A.
3. Closing an instance of scope A would close all instances of B, which were created from it (i.e. child scopes)

However, that's not what's happening. In Koin 2.0, the above DSL is equivalent to:

module {
    scope(A) {
        scoped(NUMBER) { 123 }
    }

    // actually, it's not nested :(
    scope(B) {
        scoped(STRING) { get(NUMBER).toString() }
    }
}

... and at runtime, the get(NUMBER) will throw a NoBeanDefFoundException.

Koin should do better than that.

Describe the solution you'd like
Nested scoped should be supported. For that, two things are necessary:

1. ScopeSet needs to define fun scope similar to Module.
2. Scope needs to define fun createScope similar to Koin - for the nested scopes.

Describe alternatives you've considered
An alternative to nested scopes is doing extra work (like duplicating same bindings across multiple scopes - but that will break singletons)

[valeriyo]

The approach I settled on is:

module {
    scope(A) {
        scoped(NUMBER) { 123 }
    }

    scope(B) {
        scoped(STRING) { scopeA.get<Int>(NUMBER).toString() }
    }
}

where scopeA is an extension property of Scope doing something like GlobalContext.get().koin.getScope("A") - assuming, there is an instance of scope A with name "A".

[arnaudgiuliani]

the most difficult part here is to avoid mixing scope instance id and scope qualifier: The DSL allow you to define a scope with a qualifier. A scope instance id is created/given at runtime.

[arnaudgiuliani]

this will be redesign as "Scope Links", to let you establish links between your scope instances.

[aisanu]

What's the status of this "Scope Links" stuff? Anywhere i could read the docs or at least the implementation code/related PR and the architecture design for this feature?

[kpovilaitis]

any news?

[nschwermann]

Says complete in 2.1 but still not working. You can do

scope<A>{
    scoped<B>{}
    scope<C>{
           scoped<D>{
                 linkTo(A.scope) //Must be inside scope block, unfortunate if multiple scoped items in scope C depending on B
                 D(get()) //get() B from scope A
            }
     }
}

Works but not ideal