chore: clean up examples

Author: AlexanderPrendota

examples/01_introduction/01_Hello world.md

@@ -20,7 +20,7 @@ also, note that semicolons are optional.
 
 For Kotlin versions less than 1.3 `main` function must be defined with parameter:
 
-<div class="language-kotlin" theme="idea" data-min-compiler-version="1.2">
+<div class="language-kotlin" theme="idea">
 
 ```kotlin
 fun main(args: Array<String>) {

examples/05_special_classes/00_description.md

@@ -9,8 +9,8 @@ prefix each member with the instance name.
 class Configuration(var host: String = "", var port: Int = 0, var isSSL: Boolean = false) 
 
 fun main() {
-
     val configuration = Configuration() 
+    // TODO rewrite: make conform to code style
     with(configuration) {
         host = "127.0.0.1"
         port = 9000            

examples/05_special_classes/01_Data classes.md

@@ -0,0 +1,47 @@
+# Map element access
+
+`[]` operator returns value corresponding to the given key, or `null` if such a key is not present in the map  
+
+`getValue` function returns an existing value corresponding to the given key or throws an exception,
+ mentioning which key was not found.
+ 
+If the map was produced with withDefault, this function will return the default value instead of throwing an exception.
+
+<div class="language-kotlin" theme="idea">
+
+```kotlin
+fun main(args: Array<String>) {
+
+//sampleStart
+    val map = mapOf("key" to 42)
+    
+    val value1 = map["key"]                                     // 1
+    val value2 = map["key2"]                                    // 2
+
+    val value3: Int = map.getValue("key")                       // 1
+
+    val mapWithDefault = map.withDefault { k -> k.length }
+    val value4 = mapWithDefault.getValue("key2")                // 3
+    
+    try {
+        map.getValue("anotherKey")                              // 4
+    }
+    catch (e: NoSuchElementException) {
+        println("Message: $e")
+    }
+
+//sampleEnd
+
+    println("value1 is $value1")
+    println("value2 is $value2")
+    println("value3 is $value3")
+    println("value4 is $value4")
+}
+```
+
+</div>
+
+1. Produces 42 because `"key"` is present in map
+2. Produces `null` because `"key2"` is absent.
+3. Produces default value of 4 because `"key2"` is absent.
+4. Throws NoSuchElementException because `"anotherKey"` is not in the map

examples/05_special_classes/02_Enum.md

@@ -0,0 +1,49 @@
+# getOrElse
+
+Provides safe access to elements of collection. It takes index and a function that computes default value 
+in cases when index is out of bound.
+
+
+<div class="language-kotlin" theme="idea">
+
+```kotlin
+fun main() {
+
+//sampleStart
+    val list = listOf(0, 10, 20)
+    println(list.getOrElse(1) { 42 })    // 1
+    println(list.getOrElse(10) { 42 })   // 2
+//sampleEnd
+}
+```
+
+</div>
+
+1. Prints element at index `1`
+2. Prints `42` because index `10` is out of bounds 
+
+`getOrElse` can also be applied to `Map` to get value for given key. 
+
+<div class="language-kotlin" theme="idea">
+
+```kotlin
+fun main() {
+
+//sampleStart
+    val map = mutableMapOf<String, Int?>()
+    println(map.getOrElse("x") { 1 })       // 1
+    
+    map["x"] = 3
+    println(map.getOrElse("x") { 1 })       // 2
+    
+    map["x"] = null
+    println(map.getOrElse("x") { 1 })       // 1
+//sampleEnd
+}
+```
+
+</div>
+
+
+1. Prints default value because value for key `"x"` is absent
+2. Prints `3`, value for key `"x"`