about needless (unexplained) complexity using an apply method on a trait's object to create concrete subtypes of the trait. phew!

Author: tobyweston

src/main/scala/s4j/scala/chapter19/MapExample.scala

@@ -18,7 +18,7 @@ package s4j.scala.chapter19
 
 import java.util.Calendar
 
-object MapExample {
+object MapExample extends App {
 
   def age(birthYear: Int) = {
     val currentYear = Calendar.getInstance.get(Calendar.YEAR)
@@ -27,7 +27,9 @@ object MapExample {
 
   val birthdays = List(1990, 1977, 1984, 1961, 1973)
 
-  birthdays.map(age)  // = List(25, 38, 31, 54, 42)
+  val result = birthdays.map(age)
+  println(result)
+  // results in List(27, 40, 33, 56, 44) when run in 2017
 
   // written in-line
   birthdays.map(year => Calendar.getInstance.get(Calendar.YEAR) - year)

src/main/scala/s4j/scala/chapter20/Customers.scala

@@ -20,8 +20,4 @@ trait Customers extends Iterable[Customer] {
   def add(Customer: Customer)
   def find(name: String): Option[Customer]
   def findOrNull(name: String): Customer
-}
-
-object Customers {
-  def apply() = new CustomerSet()
-}
+}

src/main/scala/s4j/scala/chapter20/Example.scala

@@ -19,7 +19,7 @@ package s4j.scala.chapter20
 import s4j.scala.chapter20.CustomerDatabase.database
 
 object CustomerDatabase {
-  val database = Customers()
+  val database = new CustomerSet()
 
   val customerA = Customer("Albert", Some(Address("1a Bridge St", None)))
   val customerB = Customer("Beatriz", None)

src/main/scala/s4j/scala/chapter21/Customers.scala

@@ -20,8 +20,4 @@ trait Customers extends Iterable[Customer] {
   def add(Customer: Customer)
   def find(name: String): Option[Customer]
   def findOrNull(name: String): Customer
-}
-
-object Customers {
-  def apply() = new CustomerSet()
-}
+}

src/main/scala/s4j/scala/chapter21/Example.scala

@@ -19,7 +19,7 @@ package s4j.scala.chapter21
 import s4j.scala.chapter21.CustomerDatabase.database
 
 object CustomerDatabase {
-  val database = Customers()
+  val database = new CustomerSet()
 
   val customerA = Customer("Albert", Some(Address("1a Bridge St", None)))
   val customerB = Customer("Beatriz", None)