Add code tabs for _tour/by-name-parameters (#2564)

Author: flomebul

Diff for: _tour/by-name-parameters.md

@@ -11,13 +11,21 @@ redirect_from: "/tutorials/tour/by-name-parameters.html"
 ---
 
 _By-name parameters_ are evaluated every time they are used. They won't be evaluated at all if they are unused. This is similar to replacing the by-name parameters with the passed expressions. They are in contrast to _by-value parameters_. To make a parameter called by-name, simply prepend `=>` to its type.
+
+{% tabs by-name-parameters_1 %}
+{% tab 'Scala 2 and 3' for=by-name-parameters_1 %}
 ```scala mdoc
 def calculate(input: => Int) = input * 37
 ```
+{% endtab %}
+{% endtabs %}
+
 By-name parameters have the advantage that they are not evaluated if they aren't used in the function body. On the other hand, by-value parameters have the advantage that they are evaluated only once.
 
 Here's an example of how we could implement a while loop:
 
+{% tabs by-name-parameters_2 class=tabs-scala-version %}
+{% tab 'Scala 2' for=by-name-parameters_2 %}
 ```scala mdoc
 def whileLoop(condition: => Boolean)(body: => Unit): Unit =
   if (condition) {
@@ -32,6 +40,24 @@ whileLoop (i > 0) {
   i -= 1
 }  // prints 2 1
 ```
+{% endtab %}
+{% tab 'Scala 3' for=by-name-parameters_2 %}
+```scala
+def whileLoop(condition: => Boolean)(body: => Unit): Unit =
+  if condition then
+    body
+    whileLoop(condition)(body)
+
+var i = 2
+
+whileLoop (i > 0) {
+  println(i)
+  i -= 1
+}  // prints 2 1
+```
+{% endtab %}
+{% endtabs %}
+
 The method `whileLoop` uses multiple parameter lists to take a condition and a body of the loop. If the `condition` is true, the `body` is executed and then a recursive call to whileLoop is made. If the `condition` is false, the body is never evaluated because we prepended `=>` to the type of `body`.
 
 Now when we pass `i > 0` as our `condition` and `println(i); i-= 1` as the `body`, it behaves like the standard while loop in many languages.