# Kotlin Crash Note

# Cheat Sheet
- Random number from 0 to 200

    (0..200).random()

- Random UUID

    UUID.randomUUID().toString()

- Hash the content

    title.hashCode().toString()

- padLeft

    val seconds:String = "9"
    print(seconds.padLeft(2,'0')) // 02
    print(seconds.padStart(2,'0')) // 20

# Generic Type
**Like `Any` in Typescript**
accept any type

fun <T> printItem(item: T) {
    println("Item: $item")
}

fun main() {
    printItem("Hello") // Item: Hello
    printItem(42)      // Item: 42
    printItem(true)    // Item: true
}

# Scope
[Reference article](https://andyludeveloper.medium.com/kotlin%E5%AD%B8%E7%BF%92%E7%AD%86%E8%A8%98-7-%E6%A8%99%E6%BA%96%E5%87%BD%E6%95%B8-scope-functions-fd1a1c394a2d)
## `apply`
for simplified the code by avoid writing the object over and over again, `apply` pass the object it self into the scope

class Person {
    var name: String = "name"
    var age: Int = 16
}

val person = Person()
person.apply {
    name = "elias"
    age = 18
}

## `let`
`let` pass the object value to the scope and return the value

val name = "elias"
val uppercaseName = name.let {
    it.toUpperCase()
}

## `run`
`run` is kind of like `apply` but **with return value**

// extend `apply` variable person

val welcomeMessage = person.run {
    name = "elias"
    age = 18
    "My name is $name and i'm $age years old"
}

## `with`
With required, a value must be passed, which will be provided to scope within the parentheses, and it will **have a return value**.
- syntax example

val numbers = mutableListOf(1, 2, 3)

val sum = with(numbers) {
    add(4)
    add(5)
    sum() // <- return 15
}

println(sum) // <- 15

## `also`
After completing the job, move on to something else

val numbers = mutableListOf("one", "two", "three")
numbers
    .also { println("The list elements before adding new one: $it") }
    .add("four")

## `takeIf`
If the condition returns `true`, execute the syntax after it
- EX: if `eliaschen` is more than 5 characters than go uppercase and print it out

val name = "eliaschen"
name.takeIf({it.length > 5})?.toUpperCase().let(::println)

## `takeUnless`
the opposite of `takeIf`, it only excute the syntax after it when the condition return `fasle`