[Kotlin] 유용한 kotiln Standard 라이브러리

let

- data의 null 체크를 할 때 주로 사용

val name : String? = ""

name?.let {

println("name $it length ${it.length}")

}

-> 예제

fun test() {

val name : String? = ""

name?.let {

println("name $it length ${it.length}")

} ?: let {

println("null")

}

}

Calls the specified function [block] with this value as its argument and returns its result.

public inline fun <T, R> T.let(block : (T) -> R) : R = block(this)

apply

- 생성과 동시에 값을 초기화할 때 유용

val textView = TextView(this)

textView.text = "button"

textView.setTextColor(getColor(R.color.abc_background_cache_hint_selector_material_dark))

textView.setOnClickListener { }

-> apply 적용

val textView = TextView(this).apply {

text = "button"

setTextColor(getColor(R.color.abc_background_cache_hint_selector_material_dark))

setOnClickListener { }

}

Calls the specified function [block] with this value as its receiver and returns this value.

public inline fun <T> T.apply(block : T.() -> Unit) : T { block() : return this }

run

- 이미 생성한 객체에 대하여 재 접근시 주로 사용

textView.text = "click button"

textView.setOnClickListener { }

-> 연속적인 접근을 줄여준다.

textView.run {

text = "click button"

setOnClickListener { }

}

Calls the specified function [block] with this value as its receiver and returns its result.

public inline fun <T, R> T.run(block : T.() -> R) : R = block()

with

- View에 접근할 때 주로 사용

fun onBindView() {

with(itemView) {

// ... itemView에 접근하기

}

}

Calls the specified function [block] with the given [receiver] as its receiver and returns its result.

public inline fun <T, R> with(receiver : T, block : T.() -> R) : R = receiver.block()

also

- add v1.1

Calls the specified function [block] with this value as its argument and returns this value.

public inline fun <T> T.also(block (T) -> Unit) : T { block(this) : return this }

data class Block(var name : String = "", var age : Int = 10)

fun Block.copyName(age : Int) = Block().also {

it.name = this.name

it.age = age

}

@Test

fun test() {

val block = Block("ABC")

val temp = block.copyName(20)

println("block $block temp $temp")

}

block Block(name=ABC, age=10) temp Block(name=ABC, age=20)

takeIf

- add v1.1

Returns this value if it satisfies the given [predicate] or null, if it doesn't

public inline fun <T> T.takeIf(predicate : (T) -> Boolean) : T? = if (predicate(this)) this else null

fun test() {

val block = Block("ABC")

println("out ${block.takeIf { it.age > 10 }}")

}

takeUnless

- add v1.1

Returns this value if it does not satisfies the given [predicate] or null, if it does

public inline fun <T> T.takeUnless(predicate : (T) -> Boolean) : T? = if (!predicate(this)) this else null

fun test() {

val block = Block("ABC")

println("out ${block.takeUnless { it.age > 10 }}")

}

data class Block(var name : String = "", var age : Int = 10)