Kotlin提升生产力

import java.time.LocalDate
import java.time.chrono.ChronoLocalDate

fun format(userName: String, domain: String) = "$userName@$domain"
fun findMinMax(list: List<Int>): Pair<Int, Int> { 
    // do the math
    return Pair(50, 100) 
}
data class User(val username: String, val email: String)    // 1

fun getUser() = User("Mary", "[email protected]")

class Pair<K, V>(val first: K, val second: V) {  // 1
    operator fun component1(): K {              
        return first
    }

    operator fun component2(): V {              
        return second
    }
}

fun main() {

    val date: ChronoLocalDate? = LocalDate.now()    // 1
    
    if (date != null) {
        println(date.isLeapYear)                    // 2
    }
    
    if (date != null && date.isLeapYear) {          // 3
        println("It's a leap year!")
    }
    
    if (date == null || !date.isLeapYear) {         // 4
        println("There's no Feb 29 this year...")
    }
    
    if (date is LocalDate) {
        val month = date.monthValue                 // 5
        println(month)
    }

    val (num, name) = Pair(1, "one")             // 2

    println("num = $num, name = $name")


    val user = getUser()
    val (username, email) = user                            // 2
    println(username == user.component1())                  // 3

    val (_, emailAddress) = getUser()                       // 4

    val (x, y, z) = arrayOf(5, 10, 15)                              // 1

    val map = mapOf("Alice" to 21, "Bob" to 25)
    for ((name, age) in map) {                                      // 2
        println("$name is $age years old")          
    }

    val (min, max) = findMinMax(listOf(100, 90, 50, 98, 76, 83))    // 3



    val greeting = "Kotliner"
    
    println("Hello $greeting")                  // 1 
    println("Hello ${greeting.uppercase()}")    // 2

    println(format("mario", "example.com"))                         // 1
    println(format("domain.com", "username"))                       // 2
    println(format(userName = "foo", domain = "bar.com"))           // 3
    println(format(domain = "frog.com", userName = "pepe"))         // 4

}