Simplified beans definition

[qwert2603]

Hello!

Motivation

One of the advantages of annotations-based DI is that it does not require to edit DI-related code, when parameters are added or removed from @Inject constructor. For example, Daggers consumes such changes automatically. It would be great to add such possibility to Koin.

Solution

One of the possible solutions may look like this:

import org.koin.core.definition.BeanDefinition
import org.koin.core.module.Module
import org.koin.core.qualifier.Qualifier
import org.koin.dsl.module

inline fun <reified T> Module.single(
    crossinline creator: () -> T,
    qualifier: Qualifier? = null,
    createdAtStart: Boolean = false,
    override: Boolean = false,
): BeanDefinition<T> = single(qualifier, createdAtStart, override) {
    creator()
}

inline fun <reified P0, reified T> Module.single(
    crossinline creator: (P0) -> T,
    qualifier: Qualifier? = null,
    createdAtStart: Boolean = false,
    override: Boolean = false,
): BeanDefinition<T> = single(qualifier, createdAtStart, override) {
    creator(get())
}

inline fun <reified P0, reified P1, reified T> Module.single(
    crossinline creator: (P0, P1) -> T,
    qualifier: Qualifier? = null,
    createdAtStart: Boolean = false,
    override: Boolean = false,
): BeanDefinition<T> = single(qualifier, createdAtStart, override) {
    creator(get(), get())
}

class SomeRepo(val argumentOne: Int)

val someModule = module {
    single(::SomeRepo)
}

With such approach we can remove argumentOne from SomeRepo's constructor or add argumentTwo without any changes in Koin's module definition.

The same can be applied to factory, scoped and other BeanDefinition creators. Moreover, it works well with any method references, not only with constructors.

Limitations

But there are limitations. There is no easy way to specify DefinitionParameters or Qualifier of individual dependency of the bean.

Feedback is welcome.

In comments.

[arnaudgiuliani]

Closing this, as another PR is fixing it