Why it's not always possible to use constructor DSL to declare a bean just by its interface?

[goshki]

Constructor DSL (singleOf, factoryOf) operates on refied types but in some cases it doesn't work as expected. Consider the following code:

class A

interface I1
class B : I1

interface I2
class C(a: A): I2

interface I3
class D(i: I1): I3

val module = module {
    singleOf(::A) // OK, injected as A
    singleOf<I1>(::B) // OK, injected as I1
    singleOf<I2>(::C) // ERROR: None of the following functions can be called with the arguments supplied.
    singleOf<I3>(::D) // ERROR: None of the following functions can be called with the arguments supplied.
}

As soon as the constructor has any parameter, Kotlin compiler cannot match a proper version of singleOf or factoryOf. I know I can define injections as:

singleOf(::C) { bind<I2>() }

but the result is that there will be two injections available: C and I2 (and it's not as clean as I would like it to be 😉).

P.S.: I'm using Koin 3.4.0.

[arnaudgiuliani]

effectively, you can't use a reified type to infer the given type directly. The idea of the Ctor DSL is to point to a function or a constructor to build an instance. In the way the API is written, it seems to let you write singleOf<I1>(::B), but I'm afraid it's a case to confirm with the kotlin team after that.

For now, consider using explicit bind

[goshki]

Thank you for the explanation. So if I understand correctly, it basically pins down to the fact that I'm trying to use the Constructor DSL not according to its intended usage and just accidentally singleOf<I1>(::B) happens to work as I was expecting?

[arnaudgiuliani]

yes 👍 kindof IDE/Kotlin magic

[dbaronne]

Hello, I think is not an IDE/Kotlin magic, it's just that your B class has no parameter so you can specify the infered type

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.