/**
 * Calls the specified function [block] with `this` value as its receiver and returns `this` value.
 *
 * For detailed usage information see the documentation for [scope functions](https://kotlinlang.org/docs/reference/scope-functions.html#apply).
 */
@kotlin.internal.InlineOnly
public inline fun <T> T.apply(block: T.() -> Unit): T {
    contract {
        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }
    block()
    return this
}

/**
 * Calls the specified function [block] with `this` value as its argument and returns `this` value.
 *
 * For detailed usage information see the documentation for [scope functions](https://kotlinlang.org/docs/reference/scope-functions.html#also).
 */
@kotlin.internal.InlineOnly
@SinceKotlin("1.1")
public inline fun <T> T.also(block: (T) -> Unit): T {
    contract {
        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }
    block(this)
    return this
}

also 和 apply的差別主要存在于，lambda表達式內context表示方式，also是通過傳入 的參數（it）來表示的，而apply是通過this來表示的。

also 可用于不更改對象的其他操作，例如記錄或打印調試信息。通常，您可以在不破壞程序邏輯的情況下從調用鏈中刪除也是調用。

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

apply主要對接收器對象的成員進行操作。 apply的常見情況是對象配置。此類調用可以讀作“將以下賦值應用于對象"

val adam = Person("Adam").apply {
    age = 32
    city = "London"        
}