lesson 2 update

build.gradle.kts

@@ -1,5 +1,5 @@
 plugins {
-    kotlin("jvm") version "1.4.30"
+    kotlin("jvm") version "1.4.31"
 }
 
 group = "ru.mipt.npm"

src/main/kotlin/lesson2/idiom10-12.kt

@@ -8,17 +8,29 @@ import java.io.File
  */
 fun idiom10() {
     class A(val b: Boolean?)
-    val a: A = A(null)
+
+    val a: A? = A(null)
     //use
     a?.b == true
     //instead of
     a?.b ?: false
+
+    // The old way
+    val res = if (a == null) {
+        false
+    } else {
+        if (a.b == null) {
+            false
+        } else {
+            a.b
+        }
+    }
 }
 
 /**
  * Dart-like (?=) nullable assignment
  */
-fun idiom11(){
+fun idiom11() {
     var x: String? = null
     x = x ?: "Hello"
 }
@@ -26,7 +38,7 @@ fun idiom11(){
 /**
  * Safe call and elvis operator
  */
-fun idiom12(){
+fun idiom12() {
     val files = File("Test").listFiles()
     println(files?.size ?: "empty")
 }

src/main/kotlin/lesson2/idiom13.kt

@@ -2,14 +2,16 @@ package lesson2
 
 fun printNotNull(any: Any) = println(any)
 
-fun main(){
+val value: Int? = 2
-    var value: Int? = 2
 
-    if(value != null){
+fun main() {
+
+    if (value != null) {
         //not guaranteed to work with mutable variable
         printNotNull(value)
     }
 
+    // Safe call here
     value?.let {
         printNotNull(it) // execute this block if not null
         printNotNull(value) // value is not null here

src/main/kotlin/lesson2/idiom14-15.kt

@@ -5,9 +5,9 @@ package lesson2
  */
 fun String.countOs(): Int = count { it == 'о' } // implicit this points to String
 
-fun Int.printMe() = println(this) // explicit this
-
 fun main() {
+    fun Int.printMe() = println(this) // explicit this
+
     "обороноспособность".countOs().printMe()
 }
 

src/main/kotlin/lesson2/idiom6.kt

@@ -3,10 +3,11 @@ package lesson2
 //Interfaces and objects
 
 interface AnInterface {
+    val a: Int get() = 4
     fun doSomething()
 }
 
-class AClass : AnInterface {
+class AClass(override val a: Int) : AnInterface {
     override fun doSomething() = TODO()
 }
 
@@ -21,10 +22,10 @@ fun main() {
     /**
      * Creating an instance
      */
-    val instance = AClass()
+    val instance = AClass(3)
 
     /**
-     * Using singleton reference without constructor invokation
+     * Using singleton reference without constructor invocation
      */
     val obj = AnObject
 
@@ -41,4 +42,6 @@ fun main() {
     val voldemort = object {
         fun doSomething(): Unit = TODO()
     }
+
+    voldemort.doSomething()
 }

src/main/kotlin/lesson2/idiom7.kt

@@ -9,3 +9,7 @@ fun checkType(arg: Any) = when(arg){
     is Double -> println("I am a Double")
     else -> println("I don't know who am I?")
 }
+
+fun main() {
+    checkType(true)
+}

src/main/kotlin/lesson2/idiom8.kt

@@ -1,11 +1,17 @@
 package lesson2
 
-class SimpleClass(val a: Int, val b: Double)
+class SimpleClass(val a: Int, val b: Double, c: Double)
 
 
-data class DataClass(val a: Int, val b: Double)
+data class DataClass(val a: Int, val b: Double){
+    val c get() = b +1
+}
 
 fun main() {
+    val simple = SimpleClass(1,2.0,3.0)
+
+    println(simple)
+
     val data = DataClass(2, 2.0)
     val copy = data.copy(b = 22.2)
     println(copy)

src/main/kotlin/lesson2/idiom9.kt

@@ -1,5 +1,7 @@
 package lesson2
 
+import lesson1.returnUnit
+
 /**
  * The declaration if valid because [TODO] returns Nothing
  */