rstraub

def couple_train(train, train_set):
    return train + (train_set,)


def decouple_train(train):
    return train[:-1]


def train_length(train):

rstraub

class Train:
    def __init__(self, composition):
        self.composition = composition

    def couple(self, train_set):
        self.composition.append(train_set)

    def decouple(self):
        self.composition.pop()

rstraub

class Train:
    def __init__(self, composition):
        self.composition = composition

    def couple(self, train_set):
        self.composition.append(train_set)

    def decouple(self):
 self.composition.pop()

rstraub

fun Int.toWeight(): Weight = Weight(this)
fun easyConstruction() = 1000.toWeight() // Weight(1000)

rstraub

@JvmInline
value class Weight(val grams: Int) {
    operator fun plus(other: Weight) = Weight(grams + other.grams)
}

fun operatorStuff(): Weight = Weight(1000) + Weight(500) // Weight(1500)

rstraub

enum class Bean { ARABICA, ROBUSTA, BLEND }
data class Coffee(val type: Bean, val intensity: Int, val weight: Int)

rstraub

enum class Bean { ARABICA, ROBUSTA, BLEND }
enum class Intensity { ONE, TWO, THREE, FOUR, FIVE }
data class Weight(val grams: Int) { /* implementation details */ }
data class Coffee(val type: Bean, val intensity: Intensity, val weight: Weight)

rstraub

data class Weight(val grams: Int) {
    init {
        require(grams >= 0) { "Weight should be a positive number" }
    }

    fun toKilograms() = grams / 1000.0
}

rstraub

data class Weight(val grams: Int) {
    init {
        require(grams >= 0) { "Weight should be a positive number" }
    }
}

rstraub

// Checks validity of weight
fun inputA(weight: Int) {
    require(weight >= 0) { "Weight should be a positive number" }
    // Logic with weight
}

// Also checks the validity of weight: duplication!
fun inputB(weight: Int) {
    // Because the checks are implemented in different ways it's harder to spot.
    if (weight < 0) throw IllegalArgumentException("Weight should be a positive number")