When expressions

The when expression is a switch-case in other languages like JavaScript but more powerful than the latter.

When a when statement is used as an expression, the compiler will require that the when statement is exhaustive, covering all possible input.

val race = "Hylian"

val popularCharacter = when (race) {
  // this is using the `==` operator for comparison
  "Hylian", "Human" -> "Link"
  "Sheikah" -> "Impa"
  "Zora" -> "Ruto"
  else -> {
    // This `else` branch adds a fallback option to satisfy
    // the compiler regarding the exhaustive behavior of `when`
    "Tingle"
  }
}

When expressions with variable declarations

Sometimes, we will use a when expression with an argument that we compute only for the sake of using it inside the when expression.

val playerLevel = experience/100 + 1
val playerTitle = when (playerLevel) {
  1 -> "Noob"
  in 2..10 -> "Level $playerLevel Chad"
  else -> "Doge Knight"
}

The previous code can be refactored like this, making the playerLevel variable scoped only inside the when statement.

val playerTitle = when (val playerLevel = experience/100 + 1) {
  // ...
}

When expressions without arguments

A when statement without an argument is an interchangeable if/else statement

val status = when {
  experience > requiredExperience -> "Get more experience!"
  experience == requiredExperience -> "You can level up!"
  requiredExperience - experience < 25 -> {
    "You're almost there, keep getting experience"
  }
}