Kotlin Nullable Type zero overhead

KotlinNullableTypeZeroOverhead.kt

// Kotlin NullableType is different from java.util.Optional or scala.Option
// it is NOT a Value Type

var str: String? = null

str == null // Compile OK! => true 

str = "gary"  // Compile OK! 

str == null // Compile OK! => false
str == "gary" // Copmile OK! => true

// Optional chaining
str?.toUpperCase() == "GARY" // Compile OK! => true
str?.toLowerCase()?.capitalize() == "Gary" // Compile OK! => true

// Default value `?:`
val username = str ?: "N/A" // username is String now!

// Kotlin Smart cast - if
if(str is String){
   // the Type of str is smart casted to `String`!!!
   println(str.toUpperCase())
}

// Kotlin Smart cast - when
when(str){
  is String -> println(str.toUpperCase()) 
  else -> println("str is null")
}