Merge pull request #2599 from smarter/codetabs1

Add code tabs for _overviews/scala3-book/types-{introduction,generics}.md

Author: bishabosha

_overviews/scala3-book/types-generics.md

@@ -13,6 +13,30 @@ Generic classes (or traits) take a type as _a parameter_ within square brackets
 The Scala convention is to use a single letter (like `A`) to name those type parameters.
 The type can then be used inside the class as needed for method instance parameters, or on return types:
 
+{% tabs stack class=tabs-scala-version %}
+
+{% tab 'Scala 2' %}
+```scala
+// here we declare the type parameter A
+//          v
+class Stack[A] {
+  private var elements: List[A] = Nil
+  //                         ^
+  //  Here we refer to the type parameter
+  //          v
+  def push(x: A): Unit =
+    elements = elements.prepended(x)
+  def peek: A = elements.head
+  def pop(): A = {
+    val currentTop = peek
+    elements = elements.tail
+    currentTop
+  }
+}
+```
+{% endtab %}
+
+{% tab 'Scala 3' %}
 ```scala
 // here we declare the type parameter A
 //          v
@@ -21,26 +45,42 @@ class Stack[A]:
   //                         ^
   //  Here we refer to the type parameter
   //          v
-  def push(x: A): Unit = { elements = elements.prepended(x) }
+  def push(x: A): Unit =
+    elements = elements.prepended(x)
   def peek: A = elements.head
   def pop(): A =
     val currentTop = peek
     elements = elements.tail
     currentTop
 ```
+{% endtab %}
+{% endtabs %}
 
 This implementation of a `Stack` class takes any type as a parameter.
 The beauty of generics is that you can now create a `Stack[Int]`, `Stack[String]`, and so on, allowing you to reuse your implementation of a `Stack` for arbitrary element types.
 
 This is how you create and use a `Stack[Int]`:
 
+{% tabs stack-usage class=tabs-scala-version %}
+{% tab 'Scala 2' %}
+```
+val stack = new Stack[Int]
+stack.push(1)
+stack.push(2)
+println(stack.pop())  // prints 2
+println(stack.pop())  // prints 1
+```
+{% endtab %}
+{% tab 'Scala 3' %}
 ```
 val stack = Stack[Int]
 stack.push(1)
 stack.push(2)
 println(stack.pop())  // prints 2
 println(stack.pop())  // prints 1
 ```
+{% endtab %}
+{% endtabs %}
 
 > See the [Variance section][variance] for details on how to express variance with generic types.
 

_overviews/scala3-book/types-inferred.md

@@ -11,22 +11,32 @@ next-page: types-generics
 
 As with other statically typed programming languages, in Scala you can _declare_ a type when creating a new variable:
 
+{% tabs xy %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 val x: Int = 1
 val y: Double = 1
 ```
+{% endtab %}
+{% endtabs %}
 
 In those examples the types are _explicitly_ declared to be `Int` and `Double`, respectively.
 However, in Scala you generally don’t have to declare the type when defining value binders:
 
+{% tabs abm %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 val a = 1
 val b = List(1, 2, 3)
 val m = Map(1 -> "one", 2 -> "two")
 ```
+{% endtab %}
+{% endtabs %}
 
 When you do this, Scala _infers_ the types, as shown in the following REPL interaction:
 
+{% tabs abm2 %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 scala> val a = 1
 val a: Int = 1
@@ -37,5 +47,7 @@ val b: List[Int] = List(1, 2, 3)
 scala> val m = Map(1 -> "one", 2 -> "two")
 val m: Map[Int, String] = Map(1 -> one, 2 -> two)
 ```
+{% endtab %}
+{% endtabs %}
 
 Indeed, most variables are defined this way, and Scala’s ability to automatically infer types is one feature that makes it _feel_ like a dynamically typed language.

_overviews/scala3-book/types-introduction.md

@@ -12,19 +12,27 @@ next-page: types-inferred
 Scala is a unique language in that it’s statically typed, but often _feels_ flexible and dynamic.
 For instance, thanks to type inference you can write code like this without explicitly specifying the variable types:
 
+{% tabs hi %}
+{% tab 'Scala 2 and 3' %}
 ```scala
 val a = 1
 val b = 2.0
 val c = "Hi!"
 ```
+{% endtab %}
+{% endtabs %}
 
 That makes the code feel dynamically typed.
 And thanks to new features, like [union types][union-types] in Scala 3, you can also write code like the following that expresses very concisely which values are expected as arguments and which types are returned:
 
+{% tabs union-example %}
+{% tab 'Scala 3 Only' %}
 ```scala
 def isTruthy(a: Boolean | Int | String): Boolean = ???
 def dogCatOrWhatever(): Dog | Plant | Car | Sun = ???
 ```
+{% endtab %}
+{% endtabs %}
 
 As the example suggests, when using union types, the types don’t have to share a common hierarchy, and you can still accept them as arguments or return them from a method.