Tiny compile time dependency injection framework for Scala

factorio

Basic assumptions

• everything is a singleton by default
• compile time checking for dependency graph correctness

As of version 0.3.1 factorio supports scalajs.

Usage

Installation

val factorioVersion = "0.3.1"

libraryDependencies ++= Seq(
  "io.mwielocha" %% "factorio-core" % factorioVersion,
  "io.mwielocha" %% "factorio-annotations" % factorioVersion,
  "io.mwielocha" %% "factorio-macro" % factorioVersion % "provided"
)

Options

For debugging puproses it's possible to enable compiler log that will print out generated assembler code:

// in project
scalacOptions ++= Seq(
    "-Xmacro-settings:factorio-verbose"
  )

Basic constructor composition

import factorio._

class Repository
class Service(val repository: Repository)

class App(service: Service)

val assembler = Assembler[App](Blank)

val app = assembler()

// new App(new Service(new Repository)))

Blueprints

You can configure couplings with a blueprint. A blueprint is in short a single class, or a chain of mixed traits marked by @blueprint annotation that holds provider methods or concrete type bindings:

import factorio._

class Repository
class Service(val repository: Repository)

class App(service: Service)

@blueprint
class Blueprint {
  
  @provides
  def createService(repository: Repository): Service = {
    new Service(repository)
  }
}

val assembler = Assembler[App](new Blueprint)

val app = assembler()

// val blueprint = new Blueprint
// new App(blueprint.createService(new Repository)))

You can also simply bind implementations to super classes or interfaces:

import factorio._

class Repository
trait Service
class ServiceImpl(val repository: Repository) extends Service

class App(service: Service)

@blueprint
@binds[Service to ServiceImpl]
class Blueprint { }

val assembler = Assembler[App](new Blueprint)

val app = assembler()

// val blueprint = new Blueprint
// new App(new ServiceImpl(new Repository)))

An alternative bind syntax, more similar to existing runtime based di frameworks:

import factorio._

class Repository
trait Service
class ServiceImpl(val repository: Repository) extends Service

class App(service: Service)

@blueprint
class Blueprint {
  
  val serviceBinder = bind[Service].to[ServiceImpl]

}

val assembler = Assembler[App](new Blueprint)

val app = assembler()

// val blueprint = new Blueprint
// new App(new ServiceImpl(new Repository)))

Blueprints can be composed of various traits but only traits that are marked with @blueprint will be searched for binders and providers:

import factorio._

class Database
class Repository(val database: Database)
class Service(val repository: Repository)

class App(service: Service)

@blueprint
trait RepositoryBlueprint {

  @provides
  def createRepository: Repository = {
    new Repository(new Database)
  }
}

@blueprint
trait ServiceBlueprint {
  
  @provides
  def createService(repository: Repository): Service = {
    new Service(repository)
  }
}

class Blueprint extends ServiceBlueprint with RepositoryBlueprint

val assembler = Assembler[App](new Blueprint)

val app = assembler()

// val blueprint = new Blueprint
// new App(blueprint.createService(blueprint.createRepository)))

Blueprint traits will be searched in order of natural scala mixin linearization. This makes it tricky to override binders and providers by just the order of mixin-in traits. To make an explicit override you can use @overrides annotation that will always make the selected binder or provider a priority one. Bear in mind that having multiple configurations for one type yields a warning but two configurations with @overrides annotation will yield a compile time error. Note: it is advised to only use @overrides in tests, never in production code.

import factorio._

class Database
trait Repository
class RepositoryImpl(val database: Database) extends Repository
class Service(val repository: Repository)

class App(service: Service)

@blueprint
trait RepositoryBlueprint {

  @provides
  def createRepository: Repository = {
    new RepositoryImpl(new Database)
  }
}

@blueprint
trait ServiceBlueprint {
  
  @provides
  def createService(repository: Repository): Service = {
    new Service(repository)
  }
}

trait Blueprint extends ServiceBlueprint with RepositoryBlueprint

val assembler = Assembler[App](new Blueprint {})

val app = assembler()

// val blueprint = new AppBlueprint
// new App(blueprint.createService(blueprint.createRepository)))


class DummyRepository extends Repository

@blueprint
@binds[Repository to DummyRepository]
trait TestRepositoryBlueprint

// this will overwirte reposiry provider from `RepositoryBlueprint`
trait TestBlueprint extends TestRepositoryBlueprint with Blueprint 

val testAssembler = Assembler[App](new TestBlueprint {})

val testApp = testAssembler()

// val blueprint = new TestBlueprint
// new App(blueprint.createService(new DummyRepository)))

You can also provide multiple implementations for the same types with the @named discriminator:

import factorio._

class Repository

trait Service
class ServiceImpl(val repository: Repository) extends Service

class App(
 @named("that") thatService: Service, 
 @named("other") otherService: Service
)

@blueprint
class AppBlueprint {
  
  @provides
  @named("that")
  def thatService(repository: Repository) =
    new ServiceImpl(repository) 
  
  @provides
  @named("other")
  def otherService(repository: Repository) =
    new ServiceImpl(repository)

}

val assembler = Assembler[App](new AppBlueprint)

val app = assembler()

// val blueprint = new AppBlueprint
// val repository = new Repository
// new App(
//   blueprint.thatService(repository), 
//   blueprint.otherService(repository))
// )

Scala style @named annotation can be replaced with javax.inject.Named

Non-singleton components

Following on the assumption that everything is a Singleton we need to reverse javax.inject logic and introduce a non-singleton annotation @replicated:

import factorio._

@replicated
class Repository
class Service(val repository: Repository)

class App(service: Service)

val assembler = Assembler[App](Blank)

val app = assembler()

// repository is now a def so new instance is injected to every parent
// def repository = new Repository 
// new App(new Service(repository)))

Dependency graph correctness

Factorio will validate the corectness of the dependency graph in compile time and will abort compilation on any given error:

import factorio._

class CircularDependency(val dependency: OuterCircularDependency)

class OuterCircularDependency(val dependency: CircularDependency)

Assembler[CircularDependency](Blank)

//[error] [Factorio]: Circular dependency detected: factorio.CircularDependency -> factorio.OuterCircularDependency -> factorio.CircularDependency
//[error]
//[error]     Assembler[CircularDependency](Blank)
//[error]                                 ^
//[error] one error found

or if there is no constructor nor recipe for the given type:

import factorio._

class Repository
trait Service
class ServiceImpl(val repository: Repository) extends Service

class App(service: Service)

Assembler[App](Blank)

//[error] [Factorio]: Cannot construct an instance of [factorio.Service]
//[error]
//[error]     Assembler[App](Blank)
//[error]                  ^
//[error] one error found