Merge pull request #2497 from Sporarum/update-singleton-objects

Update singleton-objects.md to use scala 2/3 tabs

Author: julienrf

_tour/singleton-objects.md

@@ -16,23 +16,52 @@ As a top-level value, an object is a singleton.
 As a member of an enclosing class or as a local value, it behaves exactly like a lazy val.
 # Defining a singleton object
 An object is a value. The definition of an object looks like a class, but uses the keyword `object`:
+
+
+{% tabs object-definition-box %}
+
+{% tab 'Scala 2 and 3' for=object-definition-box %}
 ```scala mdoc
 object Box
 ```
+{% endtab %}
+
+{% endtabs %}
 
 Here's an example of an object with a method:
-```
+{% tabs singleton-logger-example class=tabs-scala-version %}
+
+{% tab 'Scala 2' for=singleton-logger-example %}
+
+```scala
 package logging
 
 object Logger {
   def info(message: String): Unit = println(s"INFO: $message")
 }
 ```
+{% endtab %}
+
+{% tab 'Scala 3' for=singleton-logger-example %}
+
+```scala
+package logging
+
+object Logger:
+  def info(message: String): Unit = println(s"INFO: $message")
+```
+{% endtab %}
+
+{% endtabs %}
+
 The method `info` can be imported from anywhere in the program. Creating utility methods like this is a common use case for singleton objects.
 
 Let's see how to use `info` in another package:
+{% tabs singleton-usage-example class=tabs-scala-version %}
 
-```
+{% tab 'Scala 2' for=singleton-usage-example %}
+
+```scala
 import logging.Logger.info
 
 class Project(name: String, daysToComplete: Int)
@@ -43,6 +72,24 @@ class Test {
   info("Created projects")  // Prints "INFO: Created projects"
 }
 ```
+{% endtab %}
+
+{% tab 'Scala 3' for=singleton-usage-example %}
+
+```scala
+import logging.Logger.info
+
+class Project(name: String, daysToComplete: Int)
+
+class Test:
+  val project1 = Project("TPS Reports", 1)
+  val project2 = Project("Website redesign", 5)
+  info("Created projects")  // Prints "INFO: Created projects"
+```
+{% endtab %}
+
+{% endtabs %}
+
 
 The `info` method is visible because of the import statement, `import logging.Logger.info`.
 
@@ -53,8 +100,11 @@ Note: If an `object` is not top-level but is nested in another class or object,
 ## Companion objects
 
 An object with the same name as a class is called a _companion object_. Conversely, the class is the object's companion class. A companion class or object can access the private members of its companion. Use a companion object for methods and values which are not specific to instances of the companion class.
-```
-import scala.math._
+{% tabs companion-object-circle class=tabs-scala-version %}
+
+{% tab 'Scala 2' for=companion-object-circle %}
+```scala
+import scala.math.pow
 
 case class Circle(radius: Double) {
   import Circle._
@@ -69,10 +119,34 @@ val circle1 = Circle(5.0)
 
 circle1.area
 ```
+{% endtab %}
+
+{% tab 'Scala 3' for=companion-object-circle %}
+```scala
+import scala.math.pow
+
+case class Circle(radius: Double):
+  import Circle.*
+  def area: Double = calculateArea(radius)
+
+object Circle:
+  private def calculateArea(radius: Double): Double = Pi * pow(radius, 2.0)
+
+
+val circle1 = Circle(5.0)
+
+circle1.area
+```
+{% endtab %}
+
+{% endtabs %}
 
 The `class Circle` has a member `area` which is specific to each instance, and the singleton `object Circle` has a method `calculateArea` which is available to every instance.
 
 The companion object can also contain factory methods:
+{% tabs companion-object-email class=tabs-scala-version %}
+
+{% tab 'Scala 2' for=companion-object-email %}
 ```scala mdoc
 class Email(val username: String, val domainName: String)
 
@@ -95,6 +169,31 @@ scalaCenterEmail match {
   case None => println("Error: could not parse email")
 }
 ```
+{% endtab %}
+
+{% tab 'Scala 3' for=companion-object-email %}
+```scala
+class Email(val username: String, val domainName: String)
+
+object Email:
+  def fromString(emailString: String): Option[Email] = 
+    emailString.split('@') match
+      case Array(a, b) => Some(Email(a, b))
+      case _ => None
+
+val scalaCenterEmail = Email.fromString("scala.center@epfl.ch")
+scalaCenterEmail match
+  case Some(email) => println(
+    s"""Registered an email
+       |Username: ${email.username}
+       |Domain name: ${email.domainName}
+     """.stripMargin)
+  case None => println("Error: could not parse email")
+```
+{% endtab %}
+
+{% endtabs %}
+
 The `object Email` contains a factory `fromString` which creates an `Email` instance from a String. We return it as an `Option[Email]` in case of parsing errors.
 
 Note: If a class or object has a companion, both must be defined in the same file. To define companions in the REPL, either define them on the same line or enter `:paste` mode.