traitのmix-inと依存性注入について（備忘録） ref: http://qiita.com/mather314/items/d0165374f657e42c35e0

file0.scala

trait Greeter {
  def greetTo(to: String): String
}

class HelloGreeter(name: String) extends Greeter {
  def greetTo(to: String) = s"${name} says 'Hello ${to}!'"
}

new HelloGreeter("Alice").greetTo("Bob") //=> Alice says 'Hello Bob!'

file1.scala

trait Greeter {
  def greetTo(to: String): String
}

trait AbstractGreeter extends Greeter {
  def name: String
  def greet: String
  def greetTo(to: String) = s"${name} says '${greet} ${to}!'"
}

class HelloGreeter(val name: String) extends AbstractGreeter {
  val greet: String = "Hello"
}

new HelloGreeter("Alice").greetTo("Bob") //=> Alice says 'Hello Bob!'

(new AbstractGreeter { def name = "Alice"; def greet = "Hi" }).greetTo("Bob") //=> Alice says 'Hi Bob!'

file2.scala

trait Greeter {
  def greetTo(to: String): String
}

trait AbstractEnglishGreeter extends Greeter {
  def name: String
  def greet: String
  def greetTo(to: String) = s"${name} says '${greet} ${to}!'"
}

trait AbstractJapaneseGreeter extends Greeter {
  def name: String
  def greet: String
  def greetTo(to: String) = s"${name} は'${greet} ${to}!'と言いました"
}

class HelloEnglishGreeter(val name: String) extends AbstractEnglishGreeter {
  val greet: String = "Hello"
}

class HelloJapaneseGreeter(val name: String) extends AbstractJapaneseGreeter {
  val greet: String = "Hello"
}

file3.scala

trait Greeter {
  def greetTo(to: String): String
}

trait AbstractGreeter extends Greeter {
  def name: String
  def greet: String
}

trait EnglishGreeter extends AbstractGreeter {
  def greetTo(to: String) = s"${name} says '${greet} ${to}!'"
}

trait JapaneseGreeter extends AbstractGreeter {
  def greetTo(to: String) = s"${name} は'${greet} ${to}!'と言いました"
}

class HelloGreeter(val name: String) {
  // コンパイル時にmix-inが必要なレイヤー
  this: AbstractGreeter => 
  val greet: String = "Hello"

  // AbstractGreeter のメソッドを利用できる
  def yellTo(to: String) = greetTo(to).toUpperCase
}

val alice = new HelloGreeter("Alice") with JapaneseGreeter
alice.greetTo("Bob") //=> Alice は'Hello Bob!'と言いました
alice.yellTo("Bob")  //=> ALICE は'HELLO BOB!'と言いました

file4.scala

val userService: UserService = ???
val alice: User = userService.getById("Alice")
val result: Boolean = userService.activate(alice)

file5.scala

class User

trait UserDao {
  def dbHost: String
  def dbName: String
  def getById(id: String): User
}
trait PostgresUserDao extends UserDao {
  def getById(id: String): User = ...
}

trait UserActivator {
  def activate(user: User): Boolean
}
trait LDAPUserActivator extends UserActicator {
  def activate(user: User): Boolean = ...
}

class UserService {
  this: UserDao with UserActivator => 
}

// 実装の配線と設定値の挿入
val userService = new UserService extends PostgresUserDao with LDAPUserActivator {
  val dbHost = "192.168.1.1"
  val dbName = "db1"
}