Add package objects docs [tutorial] {EN}

_tour/package-objects.md

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+---
+layout: tour
+title: Package Objects
+
+discourse: true
+
+partof: scala-tour
+
+num: 35
+previous-page: packages-and-imports
+---
+
+# Package Objects
+Scala provides you package object as convenient container shared across the package. Package objects
+can contain arbitrary definitions, not just variable and method definitions. For instance, they frequently
+used to hold package-wide type aliases and implicit conversions. Package objects can even inherit
+Scala classes and traits.
+
+Package objects usually created as separate scala file in the package lavel - `package.scala`
+
+Each package is allowed to have one package object. Any definitions placed in a package object are considered
+members of the package itself.
+
+See example below. Assume first a class `Fruit` and three `Fruit` objects in a package
+`gardening.fruits`:
+
+```
+// in file gardening/fruits/Fruit.scala
+package gardening.fruits
+
+case class Fruit(name: String, color: String)
+object apple extends Fruit("Apple", "green")
+object plum extends Fruit("Plum", "blue")
+object banana extends Fruit("Banana", "yellow")
+```
+Now assume you want to place a variable planted and a method `showFruit` directly into package `gardening`.
+Here's how this is done:
+```
+// in file gardening/fruits/package.scala
+package gardening
+package object fruits {
+  val planted = List(apple, plum, banana)               
+  def showFruit(fruit: Fruit) {
+    println(fruit.name +"s are "+ fruit.color)
+  }
+}
+```
+
+Having the package Object above, any other code in the same package can import the method just like it would import
+a class. For example, the following object `PrintPlanted` imports `planted` and `showFruit` in exactly the same
+way it imports class `Fruit`, using a wildcard import on package gardening.fruits:
+
+```
+// in file PrintPlanted.scala
+import gardening.fruits._
+object PrintPlanted {
+  def main(args: Array[String]) {
+    for (fruit: Fruit <- fruits.planted) {
+      showFruit(fruit)
+    }
+  }
+}
+```
+Having package object also helps reducing number of imports on client use.
+
+Package objects are usual objects. That means you can use inheritance for building them (for exmple from traits):
+```
+package object fruits extends FruitAliases 
+                          with FruitHelpers {
+// helpers and variables follows here          
+}
+```
+Note that method overloading doesn't work in package objects.
+