Homework 2: patterns

src/main/kotlin/builder.kt

@@ -0,0 +1,15 @@
+data class Person(val firstName: String, val lastName: String)
+
+class PersonBuilder {
+
+    private lateinit var firstName: String
+    private lateinit var lastName: String
+
+    fun firstName(value: String) = this.also { firstName = value }
+
+    fun lastName(value: String) = this.also { lastName = value }
+
+    fun build() = Person(firstName, lastName)
+}
+
+fun main() = println(PersonBuilder().firstName("John").lastName("Smith").build())

src/main/kotlin/command.kt

@@ -0,0 +1,31 @@
+interface Command {
+    fun execute()
+    fun cancel()
+    fun name(): String
+}
+
+class Shell {
+    fun launch(c: Command) = c.execute()
+}
+
+class SumNumbersCommand(private vararg val args: Double?) : Command {
+    override fun execute() = println(args.filterNotNull().sum())
+
+    override fun cancel() = TODO("Not yet implemented")
+
+    override fun name(): String = "sum"
+}
+
+class SortNumbersCommand(private vararg val args: Int?) : Command {
+    override fun execute() = println(args.filterNotNull().sorted())
+
+    override fun cancel() = TODO("Not yet implemented")
+
+    override fun name(): String = "sort"
+}
+
+fun main() {
+    val shell = Shell()
+    shell.launch(SumNumbersCommand(2.5, 3.5, 8.4))
+    shell.launch(SortNumbersCommand(3, 1, 2))
+}

src/main/kotlin/decorator.kt

@@ -0,0 +1,27 @@
+abstract class MenuItem(private val previous: MenuItem?) {
+    fun process(name: String): String =
+        "${previous?.let { "${it.process(name)}, " } ?: "$name's dinner: "}${serve()}"
+
+    protected abstract fun serve(): String
+}
+
+class Soup(previous: MenuItem? = null) : MenuItem(previous) {
+    override fun serve(): String = "soup"
+}
+
+class Salad(previous: MenuItem? = null) : MenuItem(previous) {
+    override fun serve(): String = "salad"
+}
+
+class Entree(previous: MenuItem? = null) : MenuItem(previous) {
+    override fun serve(): String = "entree"
+}
+
+class Dessert(previous: MenuItem? = null) : MenuItem(previous) {
+    override fun serve(): String = "dessert"
+}
+
+fun main() {
+    println(Dessert(Entree(Salad(Soup()))).process("Anton"))
+    println(Dessert(Salad()).process("Maria"))
+}

src/main/kotlin/singleton.kt

@@ -0,0 +1,11 @@
+class Singleton private constructor() {
+
+    fun sayHello() = println("Hello from singleton")
+
+    companion object {
+        val INSTANCE by lazy(LazyThreadSafetyMode.SYNCHRONIZED) { Singleton() }
+    }
+
+}
+
+fun main() = Singleton.INSTANCE.sayHello()