refactor class/Object suite and add Pattern

Author: chirlo

Scala Intro/src/test/scala/intro/ClassPatternSuite.scala

@@ -0,0 +1,214 @@
+package intro
+
+import org.scalatest.FunSuite
+
+/**
+ * Workshop exercise showing classes and objects
+ */
+class ClassPatternSuite extends FunSuite {
+
+ //Traits are ALMOST like 'interfaces', they can't be instantiated directly
+ trait Language {
+ def isFunctional: Boolean
+ }
+
+ //This is how you can write a class, with a default constructor that takes a name
+ class LispDialect(name: String) extends Language {
+ def isFunctional = true
+ }
+
+ //objects are singletons
+ object Scala extends Language {
+ def isFunctional = true
+ }
+
+ //you can override a method with a val
+ object Java extends Language {
+ val isFunctional = false
+ }
+
+ /**
+ * How do you think an Object is accessed?
+ */
+ test("difference between class and object")({
+ val classInstance = new LispDialect("Racket")
+ assert(classInstance != null)
+
+ val objectInstance = ???
+ assert(objectInstance != null)
+ })
+
+ /**
+ * Class can contain various members. They can be variables, values and methods (procedures or functions).
+ * Return types are normally inferred by compiler, but it is a good style to used them.
+ * Types of the parameters have to be supplied to compiler in method signatures.
+ */
+ class Coder(val lang: Language = Java, var experience: Int = 0) {
+
+ // return type can be specified, don't need braces if it's just one line
+ def function(s: String, i: Int): Int = s.toInt + i
+
+ // return type can also be inferred
+ def position =
+ if (experience > 4) "Senior"
+ else "Junior"
+
+ //WARNING: Entering land of side effects !!!
+
+ // no '=' sign after definition, will return type 'Unit' which is like 'void'
+ def procedure() {
+ println("I'm just a side effect, since I return no value")
+ }
+
+ // we can return 'Unit' even using the equals sign 
+ def stillAProcedure(param: String): Unit = {
+ println("I'm still a side effect, I return Unit, even if you pass me a parameter" + param)
+ }
+
+ //some pattern matching, we'll see it in a minute
+
+ }
+
+ /**
+ * Congratulations, you just earned a year of experience
+ */
+ test("re-assign variable") {
+ val coder = new Coder
+
+ ???
+
+ assert(coder.experience == 1)
+ }
+
+ /**
+ * We need a Ruby coder with 4 years of experience, and we need him now!!!
+ */
+ test("construct an instance") {
+ val coder = new Coder(???, ???)
+
+ assert(coder.lang === ???)
+ assert(coder.experience === 4)
+
+ }
+
+ /**
+ * Can you say what the function returns?
+ * And what is the return type?
+ */
+ test("return type of function") {
+ val coder = new Coder(Scala)
+
+ val result = coder.position
+ assert(result === ???)
+ assert(result.getClass === classOf[????])
+ }
+
+ /**
+ * Class default constructor is in the the class signature and body
+ * Parameters of the default constructor can have various visibilities. In our example:
+ * - firstName is private value
+ * - lastName is public value
+ * - age is public variable
+ * For some of them compiler generates accessors/mutators, but these does not follow Java rules.
+ * They are named by fields without get/set prefixes. Using @BeanProperty annotation you can say
+ * the compiler to generate also the getter/setter pair of the methods. In case of values only
+ * accessor is generated.
+ */
+ class FamousScalaCoder(firstName: String, val lastName: String, var age: Int) extends Coder(Scala, 10) {
+
+ val fullName =
+ if (firstName == lastName) firstName
+ else firstName + lastName // expression, part of default constructor
+
+ println("And " + fullName + " was born...") // part of default constructor, too
+
+ def this(nickname: String, age: Int) = { // auxiliary constructor
+ this(nickname, nickname, age) // it has to call the default one as a 1st statement
+ }
+
+ def this(nickname: String) = { // another auxiliary constructor
+ this(nickname, -1) // it is allowed to call another auxiliary constructor as a 1st statement
+ }
+ }
+
+ /**
+ * Can you change the above mentioned class and fill the ??? in asserts to make test pass?
+ */
+ test("using default constructor and accessors/muttators")({
+ val odersky = new FamousScalaCoder("Odersky", 55)
+ odersky.age += 1
+
+ assert(odersky.age === ???)
+ assert(odersky.experience === ???)
+ })
+
+ /**
+ * We need a class ScalaCoder where you can pass the years of experience as a parameter, can you take care of that?
+ */
+ test("extending a class passing arguments to the superclass' default constructor ") {
+
+ //create a class where you can pass 
+ val you: Coder = ???
+ assert(you.lang === Scala)
+ }
+
+ /*
+ * PATTERN MATCHING
+ */
+
+ /**
+ * Pattern matching
+ *
+ * Pattern matching is like the 'switch-case' construct but much more powerful. It's a common feature of functional languages
+ * and Scala has a very neat version of it
+ *
+ */
+
+ def enjoysWork(coder: Coder) = coder.lang match {
+ case Scala => "Sure!"
+ case Java => "Less and less"
+ case l: LispDialect => "Work? what work?"
+ case _ => "not sure"
+ }
+
+ test("identify the output of a match") {
+ case class OS(name: String, version: Int)
+
+ def rate(os: OS) = os match {
+ case OS("Android", 4) => 7
+ case OS("Android", v) if v <= 4 => 6
+ case OS("Firefox OS" | "Mint", _) => 5
+ case OS("OS X", 10 | 9) => 4
+ case OS("Windows", 8) | OS("Windows ME", _) => 3
+ case _ => 0
+ }
+
+ assert(7 == rate(???))
+ assert(rate(OS("Windows", 8)) === ???)
+ assert(rate(OS("OS X", 9)) === ???)
+ assert(rate(OS("OS X", 11)) === ???)
+ assert(rate(OS("Mint", 13)) === ???)
+ assert(rate(OS("Mint", 14)) === ???)
+ assert(6 == rate(???))
+
+ }
+
+ test("write a matcher to get this results") {
+
+ def matcher(l: List[Int]) = l match {
+
+ case List(a, b, c) => 1
+
+ case _ => ???
+ }
+
+ assert(matcher(List()) == 0)
+ assert(matcher(List(0, 0, 0)) == 1)
+ assert(matcher(List(1, 1, 1)) == 1)
+ assert(matcher(List(1, 2, 3, 4)) == 2)
+ assert(matcher(List(1, 2, 4, 4, 5, 6)) == 3)
+ assert(matcher(List(3, 3, 3)) == 1)
+ assert(matcher(List(3, 3, 3, 4)) == 2)
+ }
+
+}