Yet another Koin killer :)

Modules.kt

/*
 * Copyright (c) 2022. Héctor de Isidro - hector6872
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
private val data = submodule {
  /* ... */
}
private val usecases = submodule {
  /* ... */
}

private val example = submodule {
  factory { Example(get(), get(), get()) }
  singleOf(::Example)
}

val locator = locator {
  single<Application> { App.get() }
  single<Context> { get<Application>().applicationContext }

  /* ... */
  
  submodule(data).overrideWith { flavorData }
  submodule(usecases).overrideWith { flavorUseCase }
}.overrideWith { flavorLocator }

ServiceLocator.kt

/*
 * Copyright (c) 2025. Héctor de Isidro - hector6872
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import kotlin.reflect.KClass

object ServiceLocator {
  var locator: Module = Module()
    private set

  fun create(module: Module) {
    if (locator.definitions.isNotEmpty()) error("Dependency graph already created")
    locator = module
  }
}

fun startServiceLocator(module: Module) = ServiceLocator.create(module)
fun startServiceLocator(module: Declaration) = ServiceLocator.create(locator { module() })

data class Identifier(val instanceClass: KClass<*>, val named: String) {
  override fun toString(): String = "$instanceClass" + if (named.isNotEmpty()) " named $named" else ""
}

abstract class Dependency<TYPE>(val value: () -> TYPE) {
  abstract fun get(): TYPE
}

class Factory<TYPE>(value: () -> TYPE) : Dependency<TYPE>(value) {
  override fun get(): TYPE = value()
}

class Singleton<TYPE>(value: () -> TYPE) : Dependency<TYPE>(value) {
  private val instance by lazy { value() }
  override fun get(): TYPE = instance
}

class Module internal constructor() {
  private val _definitions = mutableMapOf<Identifier, Dependency<*>>()
  val definitions: Map<Identifier, Dependency<*>> get() = _definitions.toMap()

  inline fun <reified TYPE> single(named: String? = "", override: Boolean = false, noinline instance: () -> TYPE): Identifier {
    val identifier = Identifier(TYPE::class, named.orEmpty())
    val singleton = Singleton(instance)
    updateDefinition(identifier, singleton, override)
    return identifier
  }

  inline fun <reified TYPE> factory(named: String? = "", override: Boolean = false, noinline instance: () -> TYPE): Identifier {
    val identifier = Identifier(TYPE::class, named.orEmpty())
    val factory = Factory(instance)
    updateDefinition(identifier, factory, override)
    return identifier
  }

  inline fun <reified TYPE> resolve(noinline instance: () -> TYPE): TYPE = instance()

  fun <TYPE> updateDefinition(identifier: Identifier, instance: Dependency<TYPE>, override: Boolean = false) {
    if (!override) if (definitions.containsKey(identifier)) throw DependencyCreationException("Found duplicated definition for: $identifier")
    _definitions[identifier] = instance
  }

  @Suppress("TooGenericExceptionCaught", "ThrowsCount", "SwallowedException")
  inline fun <reified RESULT> get(named: String? = ""): RESULT {
    val identifier = Identifier(RESULT::class, named.orEmpty())
    return try {
      definitions[identifier]?.get() as? RESULT ?: throw DependencyResolutionException("No definition found for: $identifier")
    } catch (error: StackOverflowError) {
      throw CyclicDependencyCreationException()
    } catch (exception: Exception) {
      when (exception) {
        is CyclicDependencyCreationException -> throw CyclicDependencyCreationException("Cyclic dependency detected while resolving: $identifier")
        else -> throw exception
      }
    }
  }
}

class DependencyCreationException(override val message: String) : RuntimeException()
class DependencyResolutionException(override val message: String) : RuntimeException()
class CyclicDependencyCreationException(msg: String = "") : RuntimeException(msg)

private typealias Declaration = Module.() -> Unit

fun locator(declaration: Declaration): Module = Module().apply(declaration)
fun module(declaration: Declaration): Module = Module().apply(declaration)
fun submodule(declaration: Declaration): Declaration = declaration
fun overrideWith(declaration: Declaration): Declaration = declaration
fun Module.submodule(alias: String = "", declaration: Declaration): Module = this.apply(declaration)
fun Module.submodule(submodule: Declaration): Module = this.apply(submodule)
fun Module.overrideWith(module: Declaration): Module = this.apply(module)

inline fun <reified TYPE> inject(named: String? = ""): Lazy<TYPE> = lazy(LazyThreadSafetyMode.SYNCHRONIZED) { ServiceLocator.locator.get(named) }
inline fun <reified TYPE> resolve(noinline instance: Module.() -> TYPE): Lazy<TYPE> = lazy(LazyThreadSafetyMode.SYNCHRONIZED) { instance(ServiceLocator.locator) }
inline fun <reified TYPE> instantiate(named: String? = ""): TYPE = ServiceLocator.locator.get(named)

ServiceLocatorTest.kt

/*
 * Copyright (c) 2022. Héctor de Isidro - hector6872
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import org.amshove.kluent.*
import org.junit.Test

class ServiceLocatorTest {
  @Test
  fun `try to resolve a circular dependency should throw CyclicDependencyCreationException`() {
    val module = module {
      single { CycleA(get()) }
      single { CycleB(get()) }
    }
    assertThatExceptionOfType(CyclicDependencyCreationException::class.java).isThrownBy { module.get<CycleA>() }
  }

  @Test
  fun `duplicate dependency definition should throw DependencyCreationException`() {
    assertThatExceptionOfType(DependencyCreationException::class.java).isThrownBy {
      module {
        single { ClazzA() }
        single { ClazzA() }
      }
    }
  }

  @Test
  fun `override duplicate dependency definition should pass ok`() {
    assertThatCode {
      module {
        single { ClazzA() }
        single(override = true) { ClazzA() }
      }
    }.doesNotThrowAnyException()
  }

  @Test
  fun `try to resolve a not defined dependency should throw DependencyResolutionException`() {
    val module = module { single { ClazzA() } }
    assertThatExceptionOfType(DependencyResolutionException::class.java).isThrownBy { module.get<CycleB>() }
  }
}

private class Clazzes {
  class ClazzA
  class ClazzB(val a: ClazzA)

  class CycleA(val b: CycleB)
  class CycleB(val a: CycleA)
}

SLFactoryOfExtensions.kt

/*
 * Copyright (c) 2022. Héctor de Isidro - hector6872
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
fun <reified RESULT, reified TYPE1, reified TYPE2, reified TYPE3> Module.instantiate(constructor: (TYPE1, TYPE2, TYPE3) -> RESULT): RESULT =
  constructor(get(), get(), get())

inline fun <reified RESULT, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4> Module.instantiate(
  constructor: (TYPE1, TYPE2, TYPE3, TYPE4) -> RESULT
): RESULT = constructor(get(), get(), get(), get())

inline fun <reified RESULT, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4, reified TYPE5> Module.instantiate(
  constructor: (TYPE1, TYPE2, TYPE3, TYPE4, TYPE5) -> RESULT
): RESULT = constructor(get(), get(), get(), get(), get())

inline fun <reified RESULT, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4, reified TYPE5, reified TYPE6> Module.instantiate(
  constructor: (TYPE1, TYPE2, TYPE3, TYPE4, TYPE5, TYPE6) -> RESULT
): RESULT = constructor(get(), get(), get(), get(), get(), get())

inline fun <reified RESULT, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4, reified TYPE5, reified TYPE6, reified TYPE7> Module.instantiate(
  constructor: (TYPE1, TYPE2, TYPE3, TYPE4, TYPE5, TYPE6, TYPE7) -> RESULT
): RESULT = constructor(get(), get(), get(), get(), get(), get(), get())

inline fun <reified RESULT, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4, reified TYPE5, reified TYPE6, reified TYPE7, reified TYPE8>
  Module.instantiate(
    constructor: (TYPE1, TYPE2, TYPE3, TYPE4, TYPE5, TYPE6, TYPE7, TYPE8) -> RESULT
  ): RESULT = constructor(get(), get(), get(), get(), get(), get(), get(), get())

inline fun <reified RESULT, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4, reified TYPE5, reified TYPE6, reified TYPE7, reified TYPE8,
  reified TYPE9> Module.instantiate(
  constructor: (TYPE1, TYPE2, TYPE3, TYPE4, TYPE5, TYPE6, TYPE7, TYPE8, TYPE9) -> RESULT
): RESULT = constructor(get(), get(), get(), get(), get(), get(), get(), get(), get())

SLInstantiateExtensions.kt

/*
 * Copyright (c) 2022. Héctor de Isidro - hector6872
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
inline fun <reified TYPE> Module.factoryOf(crossinline constructor: () -> TYPE): Identifier =
  factory(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1> Module.factoryOf(crossinline constructor: (TYPE1) -> TYPE): Identifier =
  factory(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1, reified TYPE2> Module.factoryOf(crossinline constructor: (TYPE1, TYPE2) -> TYPE): Identifier =
  factory(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1, reified TYPE2, reified TYPE3> Module.factoryOf(crossinline constructor: (TYPE1, TYPE2, TYPE3) -> TYPE): Identifier =
  factory(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4> Module.factoryOf(
  crossinline constructor: (TYPE1, TYPE2, TYPE3, TYPE4) -> TYPE
): Identifier = factory(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4, reified TYPE5> Module.factoryOf(
  crossinline constructor: (TYPE1, TYPE2, TYPE3, TYPE4, TYPE5) -> TYPE
): Identifier = factory(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4, reified TYPE5, reified TYPE6> Module.factoryOf(
  crossinline constructor: (TYPE1, TYPE2, TYPE3, TYPE4, TYPE5, TYPE6) -> TYPE
): Identifier = factory(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4, reified TYPE5, reified TYPE6, reified TYPE7> Module.factoryOf(
  crossinline constructor: (TYPE1, TYPE2, TYPE3, TYPE4, TYPE5, TYPE6, TYPE7) -> TYPE
): Identifier = factory(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4, reified TYPE5, reified TYPE6, reified TYPE7, reified TYPE8>
  Module.factoryOf(
    crossinline constructor: (TYPE1, TYPE2, TYPE3, TYPE4, TYPE5, TYPE6, TYPE7, TYPE8) -> TYPE
  ): Identifier = factory(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4, reified TYPE5, reified TYPE6, reified TYPE7, reified TYPE8, reified TYPE9>
  Module.factoryOf(
    crossinline constructor: (TYPE1, TYPE2, TYPE3, TYPE4, TYPE5, TYPE6, TYPE7, TYPE8, TYPE9) -> TYPE
  ): Identifier = factory(instance = { instantiate(constructor) })

SLSingleOfExtensions.kt

/*
 * Copyright (c) 2022. Héctor de Isidro - hector6872
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

inline fun <reified TYPE> Module.singleOf(crossinline constructor: () -> TYPE): Identifier =
  single(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1> Module.singleOf(crossinline constructor: (TYPE1) -> TYPE): Identifier =
  single(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1, reified TYPE2> Module.singleOf(crossinline constructor: (TYPE1, TYPE2) -> TYPE): Identifier =
  single(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1, reified TYPE2, reified TYPE3> Module.singleOf(crossinline constructor: (TYPE1, TYPE2, TYPE3) -> TYPE): Identifier =
  single(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4>
  Module.singleOf(crossinline constructor: (TYPE1, TYPE2, TYPE3, TYPE4) -> TYPE): Identifier = single(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4, reified TYPE5>
  Module.singleOf(crossinline constructor: (TYPE1, TYPE2, TYPE3, TYPE4, TYPE5) -> TYPE): Identifier = single(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4, reified TYPE5, reified TYPE6>
  Module.singleOf(crossinline constructor: (TYPE1, TYPE2, TYPE3, TYPE4, TYPE5, TYPE6) -> TYPE): Identifier = single(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4, reified TYPE5, reified TYPE6, reified TYPE7>
  Module.singleOf(crossinline constructor: (TYPE1, TYPE2, TYPE3, TYPE4, TYPE5, TYPE6, TYPE7) -> TYPE): Identifier =
  single(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4, reified TYPE5, reified TYPE6, reified TYPE7, reified TYPE8>
  Module.singleOf(crossinline constructor: (TYPE1, TYPE2, TYPE3, TYPE4, TYPE5, TYPE6, TYPE7, TYPE8) -> TYPE): Identifier =
  single(instance = { instantiate(constructor) })

inline fun <reified TYPE, reified TYPE1, reified TYPE2, reified TYPE3, reified TYPE4, reified TYPE5, reified TYPE6, reified TYPE7, reified TYPE8, reified TYPE9>
  Module.singleOf(crossinline constructor: (TYPE1, TYPE2, TYPE3, TYPE4, TYPE5, TYPE6, TYPE7, TYPE8, TYPE9) -> TYPE): Identifier =
  single(instance = { instantiate(constructor) })