Merge pull request #2581 from benluo/_overview/scala3-book/num9-code-tabs

add code tabs in num9

Author: bishabosha

_overviews/scala3-book/taste-modeling.md

@@ -13,12 +13,9 @@ next-page: taste-methods
 NOTE: I kept the OOP section first, assuming that most readers will be coming from an OOP background.
 {% endcomment %}
 
-
 Scala supports both functional programming (FP) and object-oriented programming (OOP), as well as a fusion of the two paradigms.
 This section provides a quick overview of data modeling in OOP and FP.
 
-
-
 ## OOP Domain Modeling
 
 When writing code in an OOP style, your two main tools for data encapsulation are _traits_ and _classes_.
@@ -38,6 +35,29 @@ Later, when you want to create concrete implementations of attributes and behavi
 
 As an example of how to use traits as interfaces, here are three traits that define well-organized and modular behaviors for animals like dogs and cats:
 
+{% tabs traits class=tabs-scala-version %}
+{% tab 'Scala 2' for=traits %}
+
+```scala
+trait Speaker {
+  def speak(): String  // has no body, so it’s abstract
+}
+
+trait TailWagger {
+  def startTail(): Unit = println("tail is wagging")
+  def stopTail(): Unit = println("tail is stopped")
+}
+
+trait Runner {
+  def startRunning(): Unit = println("I’m running")
+  def stopRunning(): Unit = println("Stopped running")
+}
+```
+
+{% endtab %}
+
+{% tab 'Scala 3' for=traits %}
+
 ```scala
 trait Speaker:
   def speak(): String  // has no body, so it’s abstract
@@ -51,26 +71,80 @@ trait Runner:
   def stopRunning(): Unit = println("Stopped running")
 ```
 
+{% endtab %}
+{% endtabs %}
+
 Given those traits, here’s a `Dog` class that extends all of those traits while providing a behavior for the abstract `speak` method:
 
+{% tabs traits-class class=tabs-scala-version %}
+{% tab 'Scala 2' for=traits-class %}
+
+```scala
+class Dog(name: String) extends Speaker with TailWagger with Runner {
+  def speak(): String = "Woof!"
+}
+```
+
+{% endtab %}
+
+{% tab 'Scala 3' for=traits-class %}
+
 ```scala
 class Dog(name: String) extends Speaker, TailWagger, Runner:
   def speak(): String = "Woof!"
 ```
 
+{% endtab %}
+{% endtabs %}
+
 Notice how the class extends the traits with the `extends` keyword.
 
 Similarly, here’s a `Cat` class that implements those same traits while also overriding two of the concrete methods it inherits:
 
+{% tabs traits-override class=tabs-scala-version %}
+{% tab 'Scala 2' for=traits-override %}
+
+```scala
+class Cat(name: String) extends Speaker with TailWagger with Runner {
+  def speak(): String = "Meow"
+  override def startRunning(): Unit = println("Yeah ... I don’t run")
+  override def stopRunning(): Unit = println("No need to stop")
+}
+```
+
+{% endtab %}
+
+{% tab 'Scala 3' for=traits-override %}
+
 ```scala
 class Cat(name: String) extends Speaker, TailWagger, Runner:
   def speak(): String = "Meow"
   override def startRunning(): Unit = println("Yeah ... I don’t run")
   override def stopRunning(): Unit = println("No need to stop")
 ```
 
+{% endtab %}
+{% endtabs %}
+
 These examples show how those classes are used:
 
+{% tabs traits-use class=tabs-scala-version %}
+{% tab 'Scala 2' for=traits-use %}
+
+```scala
+val d = new Dog("Rover")
+println(d.speak())      // prints "Woof!"
+
+val c = new Cat("Morris")
+println(c.speak())      // "Meow"
+c.startRunning()        // "Yeah ... I don’t run"
+c.stopRunning()         // "No need to stop"
+```
+
+{% endtab %}
+
+{% tab 'Scala 3' for=traits-use %}
+
 ```scala
 val d = Dog("Rover")
 println(d.speak())      // prints "Woof!"
@@ -81,15 +155,35 @@ c.startRunning()        // "Yeah ... I don’t run"
 c.stopRunning()         // "No need to stop"
 ```
 
+{% endtab %}
+{% endtabs %}
+
 If that code makes sense---great, you’re comfortable with traits as interfaces.
 If not, don’t worry, they’re explained in more detail in the [Domain Modeling][data-1] chapter.
 
-
 ### Classes
 
 Scala _classes_ are used in OOP-style programming.
 Here’s an example of a class that models a “person.” In OOP fields are typically mutable, so `firstName` and `lastName` are both declared as `var` parameters:
 
+{% tabs class_1 class=tabs-scala-version %}
+{% tab 'Scala 2' for=class_1 %}
+
+```scala
+class Person(var firstName: String, var lastName: String) {
+  def printFullName() = println(s"$firstName $lastName")
+}
+
+val p = new Person("John", "Stephens")
+println(p.firstName)   // "John"
+p.lastName = "Legend"
+p.printFullName()      // "John Legend"
+```
+
+{% endtab %}
+
+{% tab 'Scala 3' for=class_1 %}
+
 ```scala
 class Person(var firstName: String, var lastName: String):
   def printFullName() = println(s"$firstName $lastName")
@@ -100,15 +194,32 @@ p.lastName = "Legend"
 p.printFullName()      // "John Legend"
 ```
 
+{% endtab %}
+{% endtabs %}
+
 Notice that the class declaration creates a constructor:
 
+{% tabs class_2 class=tabs-scala-version %}
+{% tab 'Scala 2' for=class_2 %}
+
+```scala
+// this code uses that constructor
+val p = new Person("John", "Stephens")
+```
+
+{% endtab %}
+
+{% tab 'Scala 3' for=class_2 %}
+
 ```scala
 // this code uses that constructor
 val p = Person("John", "Stephens")
 ```
 
-Constructors and other class-related topics are covered in the [Domain Modeling][data-1] chapter.
+{% endtab %}
+{% endtabs %}
 
+Constructors and other class-related topics are covered in the [Domain Modeling][data-1] chapter.
 
 ## FP Domain Modeling
 
@@ -118,23 +229,59 @@ I didn’t include that because I didn’t know if enums are intended
 to replace the Scala2 “sealed trait + case class” pattern. How to resolve?
 {% endcomment %}
 
-When writing code in an FP style, you’ll use these constructs:
+When writing code in an FP style, you’ll use these concepts:
 
-- Enums to define ADTs
-- Case classes
-- Traits
+- Algebraic Data Types to define the data
+- Traits for functionality on the data.
 
+### Enumerations and Sum Types
 
-### Enums
+Sum types are one way to model algebraic data types (ADTs) in Scala.
+
+They are used when data can be represented with different choices.
 
-The `enum` construct is a great way to model algebraic data types (ADTs) in Scala 3.
 For instance, a pizza has three main attributes:
 
 - Crust size
 - Crust type
 - Toppings
 
-These are concisely modeled with enums:
+These are concisely modeled with enumerations, which are sum types that only contain singleton values:
+
+{% tabs enum_1 class=tabs-scala-version %}
+{% tab 'Scala 2' for=enum_1 %}
+
+In Scala 2 `sealed` classes and `case object` are combined to define an enumeration:
+
+```scala
+sealed abstract class CrustSize
+object CrustSize {
+  case object Small extends CrustSize
+  case object Medium extends CrustSize
+  case object Large extends CrustSize
+}
+
+sealed abstract class CrustType
+object CrustType {
+  case object Thin extends CrustType
+  case object Thick extends CrustType
+  case object Regular extends CrustType
+}
+
+sealed abstract class Topping
+object Topping {
+  case object Cheese extends Topping
+  case object Pepperoni extends Topping
+  case object BlackOlives extends Topping
+  case object GreenOlives extends Topping
+  case object Onions extends Topping
+}
+```
+
+{% endtab %}
+{% tab 'Scala 3' for=enum_1 %}
+
+Scala 3 offers the `enum` construct for defining enumerations:
 
 ```scala
 enum CrustSize:
@@ -147,7 +294,31 @@ enum Topping:
   case Cheese, Pepperoni, BlackOlives, GreenOlives, Onions
 ```
 
-Once you have an enum you can use it in all of the ways you normally use a trait, class, or object:
+{% endtab %}
+{% endtabs %}
+
+Once you have an enumeration you can import its members as ordinary values:
+
+{% tabs enum_2 class=tabs-scala-version %}
+{% tab 'Scala 2' for=enum_2 %}
+
+```scala
+import CrustSize._
+val currentCrustSize = Small
+
+// enums in a `match` expression
+currentCrustSize match {
+  case Small => println("Small crust size")
+  case Medium => println("Medium crust size")
+  case Large => println("Large crust size")
+}
+
+// enums in an `if` statement
+if (currentCrustSize == Small) println("Small crust size")
+```
+
+{% endtab %}
+{% tab 'Scala 3' for=enum_2 %}
 
 ```scala
 import CrustSize.*
@@ -163,20 +334,42 @@ currentCrustSize match
 if currentCrustSize == Small then println("Small crust size")
 ```
 
-Here’s another example of how to create and use an ADT with Scala:
+{% endtab %}
+{% endtabs %}
+
+Here’s another example of how to create a sum type with Scala, this would not be called an enumeration because the `Succ` case has parameters:
+
+{% tabs enum_3 class=tabs-scala-version %}
+{% tab 'Scala 2' for=enum_3 %}
+
+```scala
+sealed abstract class Nat
+object Nat {
+  case object Zero extends Nat
+  case class Succ(pred: Nat) extends Nat
+}
+```
+
+Sum Types are covered in detail in the [Domain Modeling]({% link _overviews/scala3-book/domain-modeling-tools.md %}) section of this book.
+
+{% endtab %}
+{% tab 'Scala 3' for=enum_3 %}
 
 ```scala
 enum Nat:
   case Zero
   case Succ(pred: Nat)
 ```
 
-Enums are covered in detail in the [Domain Modeling][data-1] section of this book, and in the [Reference documentation]({{ site.scala3ref }}/enums/enums.html).
+Enums are covered in detail in the [Domain Modeling]({% link _overviews/scala3-book/domain-modeling-tools.md %}) section of this book, and in the [Reference documentation]({{ site.scala3ref }}/enums/enums.html).
 
+{% endtab %}
+{% endtabs %}
 
-### Case classes
+### Product Types
+
+A product type is an algebraic data type (ADT) that only has one shape, for example a singleton object, represented in Scala by a `case` object; or an immutable structure with accessible fields, represented by a `case` class.
 
-The Scala `case` class lets you model concepts with immutable data structures.
 A `case` class has all of the functionality of a `class`, and also has additional features baked in that make them useful for functional programming.
 When the compiler sees the `case` keyword in front of a `class` it has these effects and benefits:
 
@@ -187,7 +380,6 @@ When the compiler sees the `case` keyword in front of a `class` it has these eff
 - `equals` and `hashCode` methods are generated to implement structural equality.
 - A default `toString` method is generated, which is helpful for debugging.
 
-
 {% comment %}
 NOTE: Julien had a comment about how he decides when to use case classes vs classes. Add something here?
 {% endcomment %}
@@ -196,6 +388,9 @@ You _can_ manually add all of those methods to a class yourself, but since those
 
 This code demonstrates several `case` class features:
 
+{% tabs case-class %}
+{% tab 'Scala 2 and 3' for=case-class %}
+
 ```scala
 // define a case class
 case class Person(
@@ -219,8 +414,9 @@ val p2 = p.copy(name = "Elton John")
 p2               // : Person = Person(Elton John,Singer)
 ```
 
-See the [Domain Modeling][data-1] sections for many more details on `case` classes.
-
+{% endtab %}
+{% endtabs %}
 
+See the [Domain Modeling][data-1] sections for many more details on `case` classes.
 
 [data-1]: {% link _overviews/scala3-book/domain-modeling-tools.md %}