Kotlin's Apply, Also, Run, With, Let, takeIf and takeUnless Functions Usage Exammple

ApplyAlsoRunWithLet_takeIf_takeUnlessFunctionsUsage.kt

fun main(args: Array<String>)
{
  val str = "Hello World";

  val ap: String = str.apply { require(this === str) } // it is not available in the block
  require(ap == str)

  val al: String = str.also { require(it === str) } // this is not available in the block
  require(al == str)

  val r: Set<String> = str.run { require(this === str); setOf(this) } // it is not available in the block
  val w: Set<String> = with(str) { require(this === str); setOf(this) } // it is not available in the block
  val l: Set<String> = str.let { require(it === str); setOf(it) } // this is not available in the block
  require(r == w && w == l)

  // takeIf
  // takeIf is like filter for a single value.
  // It checks whether the receiver meets the predicate, and returns the receiver, if it does or null if it doesn't.
  // Combined with an elvis-operator and early returns it allows to write constructs like:
  
  val nonEmptyOrNull = str.takeIf { it.isNotEmpty() } // this is not available in the block
  // can also be written as str.takeIf(String::isNotEmpty)
  require(nonEmptyOrNull != null)
  
  val nonEmptyOrDefaullt = "".takeIf { it.isNotEmpty() } ?: "Default"
  require(nonEmptyOrDefaullt == "Default")
  
  val nonEmptyOrReturnFromThisFun = str.takeIf { it.isNotEmpty() } ?: return
  require(nonEmptyOrReturnFromThisFun == "Hello World")
  
  val nonEmptyOrThrow = str.takeIf { it.isNotEmpty() } ?: throw IllegalArgumentException("Empty")
  require(nonEmptyOrThrow == "Hello World")

  // takeUnless
  
  val nonEmptyOrNull1 = str.takeUnless { it.isEmpty() } // this is not available in the block
  require(nonEmptyOrNull1 != null)
  
  val nonEmptyOrDefaullt1 = "".takeUnless { it.isEmpty() } ?: "Default"
  require(nonEmptyOrDefaullt1 == "Default")
  
  val nonEmptyOrReturnFromThisFun1 = str.takeUnless { it.isEmpty() } ?: return
  require(nonEmptyOrReturnFromThisFun1 == "Hello World")
  
  val nonEmptyOrThrow1 = str.takeUnless { it.isEmpty() } ?: throw IllegalArgumentException("Empty")
  require(nonEmptyOrThrow1 == "Hello World")

  println("Completed");
}