Introduction to Kotlin (for Java Developers) - Cool Features - 12. Simpler lambdas & functional programming.kt

class LambdaGoodies {

    // When the lambda expression has only one param, we use "it" to access it
    fun method1() {
        val ints = listOf(0, 1, 2, 3).filter { // note that we use CURLY braces
            it > 1
        }

        ints.forEach { println(it) }
    }

    // We don't use stream() or collect() in Kotlin
    fun method2() {
        val people = listOf( Person("John"), Person("Mary") )
        val list = people.map { it.name } // Java: people.stream().map(Person::getName).collect(Collectors.toList());
    }
    private data class Person(val name: String)

    // Lambdas & functional programming in Kotlin can simplify some common operations
    fun method3() {
        // Example #1: sorting with custom comparator
        val list = arrayListOf("asdf,", "a", "b")

        Collections.sort(list, object : Comparator<String> {
            override fun compare(o1: String?, o2: String?): Int { TODO("Not yet implemented") }
        })
        Collections.sort(list, Comparator<String>( { o1, o2 -> TODO("Not yet implemented") } ))
        Collections.sort(list, Comparator<String> { o1, o2 -> TODO("Not yet implemented") } )
        Collections.sort(list, Comparator { o1, o2 -> TODO("Not yet implemented") } )
        Collections.sort(list) { o1, o2 -> TODO("Not yet implemented") } // simplest

        list.sortWith( Comparator({ o1, o2 -> TODO("Not yet implemented") }) )
        list.sortWith( Comparator { o1, o2 -> TODO("Not yet implemented") } )
        list.sortWith({ o1, o2 -> TODO("Not yet implemented") })
        list.sortWith { o1, o2 -> TODO("Not yet implemented") } // simplest

        // Example #2: modifying several fields' values at once with "apply"
        val user = User("John", "Doe", "USA")
        user.apply {
            firstName = "Ivan"
            lastName = "Ivanov"
            country = "Bulgaria"
        }
    }
    private data class User(var firstName: String, var lastName: String, var country: String)

}