Circular dependency

A circular dependency scenario occurs when, for example, a dependency X depends on a dependency Y that depends on the dependency X.

This could occur directly or indirectly, for example, the code below shows an example of a direct circular dependency:

class DependencyA @Inject constructor(val dependencyB: DependencyB)
class DependencyB @Inject constructor(val dependencyA: DependencyA)

and the code below shows and example of indirect circular dependency:

class DependencyA @Inject constructor(val dependencyB: DependencyB)
class DependencyB @Inject constructor(val dependencyC: DependencyC)
class DependencyC @Inject constructor(val dependencyA: DependencyA)

Redin does not have a mechanism to detect circular dependencies, because even if it is possible to do, given that Redin allows Dependency Providers which resolves dependencies dynamically, it will not be possible to cover all scenarios without adding extra work to users of Redin. So circular dependencies ends up in a StackOverflowError.

If you really need to have a circular dependency, use lazy dependency resolution:

class DependencyA @Inject constructor(val dependencyB: DependencyB)
class DependencyB @Inject constructor(@LazyDep val dependencyA: Lazy<DependencyA>)

fun circularInject() {
    val injector = Redin {
        bind<DependencyA>().inSingletonScope().toImplementation<DependencyA>()
        bind<DependencyB>().inSingletonScope().toImplementation<DependencyB>()
    }

    val dependency = injector.provide<DependencyA>(scope = SINGLETON)()

}

However, we heavily discourage the use of circular dependencies, as it does not follow the separation of concerns concept.

If you have a common interface, it would be interesting to use the proxied version of lazy, as it introduces lazy initialization without Lazy type indirection:

interface DependencyA
interface DependencyB

class DependencyAImpl @Inject constructor(val dependencyB: DependencyB) : DependencyA
class DependencyBImpl @Inject constructor(@LazyDep val dependencyA: DependencyA) : DependencyB


fun circularInject() {
    val injector = Redin {
        bind<DependencyA>().inSingletonScope().toImplementation<DependencyAImpl>()
        bind<DependencyB>().inSingletonScope().toImplementation<DependencyBImpl>()
    }

    val dependency = injector.provide<DependencyA>(scope = SINGLETON)()

}