Unrelated test: A Provider variant

Author: odersky

tests/run/Providers.check

@@ -18,3 +18,11 @@ Executing query: insert into subscribers(name, email) values Daniel daniel@Rockt
 You've just been subscribed to RockTheJVM. Welcome, Martin
 Acquired connection
 Executing query: insert into subscribers(name, email) values Martin odersky@gmail.com
+
+Injected2
+You've just been subscribed to RockTheJVM. Welcome, Daniel
+Acquired connection
+Executing query: insert into subscribers(name, email) values Daniel daniel@RocktheJVM.com
+You've just been subscribed to RockTheJVM. Welcome, Martin
+Acquired connection
+Executing query: insert into subscribers(name, email) values Martin odersky@gmail.com

tests/run/Providers.scala

@@ -65,6 +65,8 @@ end Providers
   Explicit().test()
   println(s"\nInjected")
   Injected().test()
+  println(s"\nInjected2")
+  Injected2().test()
 
 /** Demonstrator for explicit dependency construction */
 class Explicit:
@@ -173,5 +175,55 @@ class Injected:
   end explicit
 end Injected
 
+/** Injected with builders in companion objects */
+class Injected2:
+  import Providers.*
+
+  case class User(name: String, email: String)
+
+  class UserSubscription(emailService: EmailService, db: UserDatabase):
+    def subscribe(user: User) =
+      emailService.email(user)
+      db.insert(user)
+  object UserSubscription:
+    def apply()(using Provider[(EmailService, UserDatabase)]): UserSubscription =
+      new UserSubscription(provided[EmailService], provided[UserDatabase])
+
+  class EmailService:
+    def email(user: User) =
+      println(s"You've just been subscribed to RockTheJVM. Welcome, ${user.name}")
+
+  class UserDatabase(pool: ConnectionPool):
+    def insert(user: User) =
+      pool.get().runQuery(s"insert into subscribers(name, email) values ${user.name} ${user.email}")
+  object UserDatabase:
+    def apply()(using Provider[(ConnectionPool)]): UserDatabase =
+      new UserDatabase(provided[ConnectionPool])
+
+  class ConnectionPool(n: Int):
+    def get(): Connection =
+      println(s"Acquired connection")
+      Connection()
+
+  class Connection():
+    def runQuery(query: String): Unit =
+      println(s"Executing query: $query")
+
+  def test() =
+    given Provider[EmailService]     = provide(EmailService())
+    given Provider[ConnectionPool]   = provide(ConnectionPool(10))
+    given Provider[UserDatabase]     = provide(UserDatabase())
+    given Provider[UserSubscription] = provide(UserSubscription())
+
+    def subscribe(user: User)(using Provider[UserSubscription]) =
+      val sub = UserSubscription()
+      sub.subscribe(user)
+
+    subscribe(User("Daniel", "daniel@RocktheJVM.com"))
+    subscribe(User("Martin", "odersky@gmail.com"))
+  end test
+end Injected2
+
+