Cake pattern. Presentation by Alex Famin at scalaby#14
2 likes1,700 views
The Cake pattern is a dependency injection pattern for Scala that uses traits to define components and their dependencies. It allows defining components and their implementations separately. An object extends the necessary component traits to resolve dependencies and provides the application object graph. The graph is constructed at compile time, ensuring type safety. However, the pattern results in boilerplate code and does not provide strong lifecycle management for the components.
![class ShoppingRobot(listProvider: ShopListProvider, location: GeoLocation) {
def goShopping() = {
val list = listProvider.get
val shop = location.findNearestShop
shop.map(buy(_, list))
}
def buy(shop:Shop, list:List[Item]) = ???
}
class ShopListProvider {
def get:List[Item] = ???
}
class GeoLocation {
def findNearestShop:Maybe[Shop] = ???
}
8
Dependencies](https://image.slidesharecdn.com/cakepattern-150330044450-conversion-gate01/85/Cake-pattern-Presentation-by-Alex-Famin-at-scalaby-14-8-320.jpg)
![trait ShopListProviderComponent {
val shopListProvider: ShopListProvider
trait ShopListProvider {
def get: List[Item]
}
}
trait GeoLocationComponent {
val geoLocation: GeoLocation
trait GeoLocation {
def findNearestShop: Maybe[Shop]
}
}
11
trait ShoppingRobotComponent {
val robot: ShoppingRobot
trait ShoppingRobot {
def goShopping: Maybe[Purchase]
}
}](https://image.slidesharecdn.com/cakepattern-150330044450-conversion-gate01/85/Cake-pattern-Presentation-by-Alex-Famin-at-scalaby-14-11-320.jpg)
![trait ShopListProviderComponentImpl extends ShopListProviderComponent {
val shopListProvider: ShopListProvider = new ShopListProviderImpl
class ShopListProviderImpl extends ShopListProvider {
override def get: List[Item] = ???
}
}
trait GeoLocationComponentImpl extends GeoLocationComponent {
val geoLocation: GeoLocation = new GeoLocationImpl
class GeoLocationImpl extends GeoLocation {
override def findNearestShop: Maybe[Shop] = ???
}
}
12](https://image.slidesharecdn.com/cakepattern-150330044450-conversion-gate01/85/Cake-pattern-Presentation-by-Alex-Famin-at-scalaby-14-12-320.jpg)
![trait ShoppingRobotComponentImpl extends ShoppingRobotComponent {
this: ShoppingRobotComponentImpl
with ShopListProviderComponent
with GeoLocationComponent
=>
val robot: ShoppingRobot = new DefaultRobot
class DefaultRobot extends ShoppingRobot {
override def goShopping: Maybe[Purchase] = {
val list = listProvider.get
val shop = location.findNearestShop
shop.map(buy(_, list))
}
}
}
13
Dependency](https://image.slidesharecdn.com/cakepattern-150330044450-conversion-gate01/85/Cake-pattern-Presentation-by-Alex-Famin-at-scalaby-14-13-320.jpg)
![object TestRegistry
extends ShoppingRobotComponentImpl
with FakeGeoLocationComponentImpl
with FakeShopListProviderComponentImpl
class Registry2(shop: Shop)
extends ShoppingRobotComponentImpl
with ShopListProviderComponentImpl
with GeoLocationComponent {
val geoLocation: GeoLocation = new GeoLocation {
override def findNearestShop: Maybe[Shop] = Some(shop)
}
}
16](https://image.slidesharecdn.com/cakepattern-150330044450-conversion-gate01/85/Cake-pattern-Presentation-by-Alex-Famin-at-scalaby-14-16-320.jpg)
Cake pattern. Presentation by Alex Famin at scalaby#14
- 2. 2
- 3. DI IoC 3
- 4. DI != IoC 4
- 5. DI <: IoC 5
- 6. Cake Pattern <: DI 6
- 7. Example 7
- 8. class ShoppingRobot(listProvider: ShopListProvider, location: GeoLocation) { def goShopping() = { val list = listProvider.get val shop = location.findNearestShop shop.map(buy(_, list)) } def buy(shop:Shop, list:List[Item]) = ??? } class ShopListProvider { def get:List[Item] = ??? } class GeoLocation { def findNearestShop:Maybe[Shop] = ??? } 8 Dependencies
- 9. object Application extends App { val shoplistProvider = new ShopListProvider(); val location = new GeoLocation(); val robot = new ShoppingRobot(shopListProvider, location); robot.goShopping } 9 InjectionConstructor
- 10. Cake pattern 10
- 11. trait ShopListProviderComponent { val shopListProvider: ShopListProvider trait ShopListProvider { def get: List[Item] } } trait GeoLocationComponent { val geoLocation: GeoLocation trait GeoLocation { def findNearestShop: Maybe[Shop] } } 11 trait ShoppingRobotComponent { val robot: ShoppingRobot trait ShoppingRobot { def goShopping: Maybe[Purchase] } }
- 12. trait ShopListProviderComponentImpl extends ShopListProviderComponent { val shopListProvider: ShopListProvider = new ShopListProviderImpl class ShopListProviderImpl extends ShopListProvider { override def get: List[Item] = ??? } } trait GeoLocationComponentImpl extends GeoLocationComponent { val geoLocation: GeoLocation = new GeoLocationImpl class GeoLocationImpl extends GeoLocation { override def findNearestShop: Maybe[Shop] = ??? } } 12
- 13. trait ShoppingRobotComponentImpl extends ShoppingRobotComponent { this: ShoppingRobotComponentImpl with ShopListProviderComponent with GeoLocationComponent => val robot: ShoppingRobot = new DefaultRobot class DefaultRobot extends ShoppingRobot { override def goShopping: Maybe[Purchase] = { val list = listProvider.get val shop = location.findNearestShop shop.map(buy(_, list)) } } } 13 Dependency
- 14. object Registry extends ShoppingRobotComponentImpl with GeoLocationComponentImpl with ShopListProviderComponentImpl object Application extends App { val robot = Registry.robot robot.goShopping } 14 Injection
- 15. object FailedRegistry extends ShoppingRobotComponentImpl with GeoLocationComponentImpl error: illegal inheritance; self-type FailedRegistry.type does not conform to ShoppingRobotComponentImpl's selftype ShoppingRobotComponentImpl with ShopListProviderComponent with GeoLocationComponent object FailedRegistry extends ShoppingRobotComponentImpl with GeoLocationComponentImpl 15
- 16. object TestRegistry extends ShoppingRobotComponentImpl with FakeGeoLocationComponentImpl with FakeShopListProviderComponentImpl class Registry2(shop: Shop) extends ShoppingRobotComponentImpl with ShopListProviderComponentImpl with GeoLocationComponent { val geoLocation: GeoLocation = new GeoLocation { override def findNearestShop: Maybe[Shop] = Some(shop) } } 16
- 17. Pros and Cons + Pure Scala + Compile time validation 17 − Boilerplate overhead − Weak lifecycle control
- 18. Q&A 18