Add code tabs for _tour/self-types (#2553)

* Add code tabs for _tour/self-types

* Update _tour/self-types.md

Yes.

Co-authored-by: Jamie Thompson <[email protected]>

Co-authored-by: Jamie Thompson <[email protected]>

Author: flomebul

_tour/self-types.md

@@ -16,6 +16,9 @@ Self-types are a way to declare that a trait must be mixed into another trait, e
 A self-type is a way to narrow the type of `this` or another identifier that aliases `this`. The syntax looks like normal function syntax but means something entirely different.
 
 To use a self-type in a trait, write an identifier, the type of another trait to mix in, and a `=>` (e.g. `someIdentifier: SomeOtherTrait =>`).
+
+{% tabs self-types_1 class=tabs-scala-version %}
+{% tab 'Scala 2' for=self-types_1 %}
 ```scala mdoc
 trait User {
   def username: String
@@ -33,5 +36,25 @@ class VerifiedTweeter(val username_ : String) extends Tweeter with User {  // We
 val realBeyoncé = new VerifiedTweeter("Beyoncé")
 realBeyoncé.tweet("Just spilled my glass of lemonade")  // prints "real Beyoncé: Just spilled my glass of lemonade"
 ```
-
 Because we said `this: User =>` in `trait Tweeter`, now the variable `username` is in scope for the `tweet` method. This also means that since `VerifiedTweeter` extends `Tweeter`, it must also mix-in `User` (using `with User`).
+
+{% endtab %}
+{% tab 'Scala 3' for=self-types_1 %}
+```scala
+trait User:
+  def username: String
+
+trait Tweeter:
+  this: User =>  // reassign this
+  def tweet(tweetText: String) = println(s"$username: $tweetText")
+
+class VerifiedTweeter(val username_ : String) extends Tweeter, User:  // We mixin User because Tweeter required it
+  def username = s"real $username_"
+
+val realBeyoncé = VerifiedTweeter("Beyoncé")
+realBeyoncé.tweet("Just spilled my glass of lemonade")  // prints "real Beyoncé: Just spilled my glass of lemonade"
+```
+Because we said `this: User =>` in `trait Tweeter`, now the variable `username` is in scope for the `tweet` method. This also means that since `VerifiedTweeter` extends `Tweeter`, it must also mix-in `User` (using `, User`).
+
+{% endtab %}
+{% endtabs %}