Merge pull request #221 from ricemery/BankAccount

Rework interface definition to cleanly show openAccount. Add HINTS.md…

exercises/bank-account/HINTS.md

@@ -0,0 +1,11 @@
+## 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 the Java synchronized block.
+
+### Common Pitfalls
+
+In Scala there are two ways to achieve mutable state: Use a "var" or a mutable object.
+Two common mistakes here are:
+- Do not use a "var" that is also a mutable object. One is enough, but not both together.
+- Don't expose the "var" or mutable object to the outside world. So make them "private" and change the mutable object into immutable before you return it as a value.

exercises/bank-account/example.scala

@@ -23,8 +23,6 @@ protected case class Account(var balance: Option[Int] = Some(0)) extends BankAcc
   }
 }
 
-object BankAccount {
-  def apply(): BankAccount = Account()
+object Bank {
+  def openAccount(): BankAccount = Account()
 }
-
-

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

@@ -0,0 +1,13 @@
+trait BankAccount {
+
+  def closeAccount(): Unit
+
+  def getBalance: Option[Int]
+
+  def incrementBalance(increment: Int): Option[Int]
+}
+
+object Bank {
+  def openAccount(): BankAccount = ???
+}
+

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)