Rework interface definition to cleanly show openAccount. Add HINTS.md with note about mutable state. Refs exercism#214

Author: ricemery

exercises/bank-account/HINTS.md

@@ -0,0 +1,4 @@
+## Hints
+
+This exercise is testing mutable state that can be accessed saftely from multiple threads. Scala provides a variety of ways to protect 
+mutable state. For developers familiar with Java concurrency, Scala can utilize the Java concurrency support such as synchronized.

exercises/bank-account/example.scala

@@ -7,24 +7,8 @@ trait BankAccount {
   def incrementBalance(increment: Int): Option[Int]
 }
 
-protected case class Account(var balance: Option[Int] = Some(0)) extends BankAccount {
-
-  private def runThreadSafe[A](block: => A): A = this.synchronized(block)
-
-  override def closeAccount(): Unit = runThreadSafe(balance = None)
-
-  override def getBalance: Option[Int] = runThreadSafe(balance)
-
-  override def incrementBalance(increment: Int): Option[Int] = runThreadSafe {
-    balance flatMap { amount =>
-      balance = Some(amount + increment)
-      balance
-    }
-  }
-}
-
-object BankAccount {
-  def apply(): BankAccount = Account()
+object Bank {
+   def openAccount(): BankAccount = ???
 }
 
 

exercises/bank-account/src/main/scala/Bank.scala

@@ -0,0 +1,30 @@
+trait BankAccount {
+
+  def closeAccount(): Unit
+
+  def getBalance: Option[Int]
+
+  def incrementBalance(increment: Int): Option[Int]
+}
+
+protected case class Account(var balance: Option[Int] = Some(0)) extends BankAccount {
+
+  private def runThreadSafe[A](block: => A): A = this.synchronized(block)
+
+  override def closeAccount(): Unit = runThreadSafe(balance = None)
+
+  override def getBalance: Option[Int] = runThreadSafe(balance)
+
+  override def incrementBalance(increment: Int): Option[Int] = runThreadSafe {
+    balance flatMap { amount =>
+      balance = Some(amount + increment)
+      balance
+    }
+  }
+}
+
+object Bank {
+   def openAccount(): BankAccount = Account()
+}
+
+

exercises/bank-account/src/test/scala/BankAccountTest.scala

@@ -3,12 +3,12 @@ import org.scalatest.{Matchers, FunSuite}
 
 class BankAccountTest extends FunSuite with Matchers with Conductors with IntegrationPatience {
   test("open account") {
-    BankAccount().getBalance should be (Some(0))
+    Bank.openAccount().getBalance should be (Some(0))
   }
 
   test("incrementing and checking balance") {
     pending
-    val acct = BankAccount()
+    val acct = Bank.openAccount()
     acct.getBalance should be (Some(0))
     acct.incrementBalance(10) should be (Some(10))
     acct.getBalance should be (Some(10))
@@ -18,7 +18,7 @@ class BankAccountTest extends FunSuite with Matchers with Conductors with Integr
 
   test("closed account should hold no balance") {
     pending
-    val acct = BankAccount()
+    val acct = Bank.openAccount()
     acct.closeAccount()
     acct.incrementBalance(10)
     acct.incrementBalance(10)
@@ -30,7 +30,7 @@ class BankAccountTest extends FunSuite with Matchers with Conductors with Integr
     val conductor = new Conductor
     import conductor._
 
-    val acct = BankAccount()
+    val acct = Bank.openAccount()
 
     thread("t1") {
       acct.incrementBalance(10)
@@ -54,7 +54,7 @@ class BankAccountTest extends FunSuite with Matchers with Conductors with Integr
     val conductor = new Conductor
     import conductor._
 
-    val acct = BankAccount()
+    val acct = Bank.openAccount()
 
     thread("t1") {
       for (a <- 1 to 10)