Ivy DI ⚡

A simple and lightweight runtime Dependency Injection (DI) container for Kotlin Multiplatform. Ivy DI is a small dependency injection library with an intuitive API and limited features.

In a nutshell, you first register dependency factory functions in the container Di.register { T() } and then get instances via Di.get<T>().

interface ArticlesDataSource
class RemoteArticlesDataSource(val client: HttpClient, val baseUrl: BaseUrlProvider)
class ArticlesRepository(val source: ArticlesDataSource)

Di.appScope {
  register { BaseUrlProvider("https://ivy-apps.com") }
  singleton { HttpClient(CIO) }
  autoWire(::RemoteArticlesDataSource)
  bind<ArticlesDataSource, RemoteArticlesDataSource>()
  autoWire(::ArticlesRepository)
}

val repo = Di.get<ArticlesRepository>() // ArticlesRepository instance created

Features

• Lightweight
• One-line setup
• Easy to use?
• Auto-wiring
• Singletons
• Bindings
• Qualifiers
• Modules
• Scopes
• Lazy intitliazation

Usage

0. Setup

You can find Ivy DI in our Maven Central repository.

Gradle (Kotlin)

implementation("com.ivy-apps:di:0.0.0")

or

Version Catalog

[libraries]
ivyApps-di = { module = "com.ivy-apps:di", version = "0.0.0" }

Replace "0.0.0" with:

That's all you need! Now let's start using Ivy DI ⚡

1. Register a dependency

class A
class B(val a: A)

Di.appScope {
  register { A() }
  register { B(a = Di.get() }
}

Instances of A and B won't be created until the dependencies are requested in the code (lazy creation).

2. Get dependency instance

// instances of B and its dependencies will be created
Di.get<B>() // instance 1 of B
Di.get<B>() // instance 2 of B

Each call to Di.get() creates a new instance for non-singleton dependencies.

3. Singleton dependencies

class Counter(var x = 0) {
  init { print("Counter created. ")
}
Di.appScope {
  singleton {
    Counter() // instance won't be created here 
  }
}

println(Di.get<Counter>().x) // Counter created. 0
Di.get<Counter>.x = 42
println(Di.get<Counter>().x) // 42

Singleton dependencies will have only one single instance that will be created on the first Di.get() call.

4. Auto-wiring

class A
class B(val a: A)
class C(val a: A, val b: B)

Di.appScope {
  autoWire(::A)
  autoWireSingleton(::B) // for singletons
  autoWire(::C)
}
Di.get<C>()

To avoid repetitive code like register { C(Di.get(), Di.get()) } it's recommended to use auto-wiring.

5. Bindings

interface Platform
class AndroidPlatform : Platform

Di.appScope {
  autoWire(::AndroidPlatform)
  bind<Platform, AndroidPlatform>()
  // equivalent to:
  // register<Platform> { AndroidPlatform() }
}
Di.get<Platform>() // AndroidPlatform instance

To bind a specific implementation to an interface (or an abstract class) use bind<Interface, Impl>(). Note: Impl must be registered in the dependency graph.

6. Named dependencies (qualifiers)

interface TimeFormatter
class H24TimeFormatter : TimeFormatter
class AmPmTimeFormatter : TimeFormatter

Di.appScope {
  autoWire(::H24TimeFormatter)
  autoWire(::AmPmTimeFormatter)
  bind<TimeFormatter, H24TimeFormatter>() // default
  bind<TimeFormatter, AmPmTimeFormatter>(named = "am-pm")
}

Di.get<TimeFormatter>() // H24TimeFormatter
Di.get<TimeFormatter>(named = "am-pm") // AmPmTimeFormatter

Sometimes we need to have different instances of the same type. To achieve this in Ivy DI, we can set qualifiers using named = "something" (you're not limited only to strings because named: Any).

Important

Your "named" qualifiers must support equality checks (hashCode + equals).

7. Modules

object DataModule : Di.Module {
  override fun init() = Di.appScope {
    singleton { HttpClient(CIO) }
    register { Json() }
    autoWire(::LoginService)
    autoWireSingleton(::AnalyticsService)
  }
}

Di.init(
  // Registers the following modules in the DI container
  modules = setOf(
    AppModule,
    DataModule,
  )
)
Di.get<LoginService>()

To re-use and encapsulate DI logic you can create Di.Modules that you can later activate via Di.init(MyModule).

Advanced Usage

1. Scopes

Ivy DI supports grouping your dependencies into scopes. This way you can manage their lifecycle and free resources as soon as they are no longer needed. AppScope and FeatureScope are built-in but you can easily define your own scopes using Di.newScope("my-scope").

data class UserInfo(val id: String, name: String)

val UserScope = Di.newScope("user")
fun Di.userScope(block: Di.Scope.() -> Unit) = Di.scope(UserScope, block) // helper function (optional)

suspend fun login() {
  val userInfo = loginInternally() // UserInfo("1", "John")
  Di.userScope {
    // Register dependencies for the lifecycle of a user
    singleton { userInfo }
  }
}

// Note: This function must be called only for logged-in users, otherwise Di.get() will throw an exception.
suspend fun dashboard() {
  // Use user related dependencies
  val userInfo = Di.get<UserInfo>()
  println("Hello, ${userInfo.name}") // "Hello, John"
}

suspend fun logout() {
  logoutInternally()
  // Frees all dependencies in UserScope
  Di.clear(UserScope) // UserInfo("1", "John") gets cleared
}

2. Multibindings 🚧

Currently not supported, investigating this use-case and whether we can support it nicely.

3. Lazy initialization

By default, all instances in Ivy DI are lazily initialized only after Di.get() is called. However, there are cases where you might want to postpone the initialization even further. You can do that by wrapping your dependency in Lazy<T> and using Di.getLazy<T>() instead.

class ArticlesDataSource(val client: Lazy<HttpClient>) {
  suspend fun fetchLatest(): List<Article> = client.value.get("url") // .value gets an instance of the HttpClient
}
class ArticlesRepository(val source: ArticlesDataSource) {
  suspend fun fetchLatest(): List<Article> = source.fetchLatest()
}

Di.appScope {
  singleton { HttpClient(CIO) }
  register {
    // autoWire won't work because you need to explicitly call Di.getLazy() instead of Di.get()
    ArticlesDataSource(Di.getLazy())
  }
  autoWire(::ArticlesRepository)
}
val repo = Di.get<ArticlesRepository>() // HttpClient instance not created
repo.fetchLatest() // HttpClient instance created

The instance of HttpClient will be created only after the ArticlesDataSource#fetchLatest() method is called.

⚠️ Limitations

Generics aren't fully supported

To avoid performance and compatibility problems we limit reflection to the bare minimum. Ivy DI uses only KClass<*> which unfortunately doesn't make a difference between the generic type of a class.

For example, if you register a factory for Container<A> and Container<B>, KClass will both treat them as just Container. As an implication, only the factory for Container<B> will be registered, and Di.get<Container<A>>() will throw an exception.

Thread-safety

The Ivy DI APIs aren't synchronized and thread-safety is a responsibility of the API user. We made this decision to keep the DI container free of Java (or 3rd party) dependencies and prioritize efficiency. We recommend registering your dependencies on the main thread.

Maintenance

The library will be maintained as long as Ivy Apps Ltd has an interest in using it. Given that Ivy DI currently has no community, the project may be abandoned in the future.