Solution: Money operations
data class Money(
val amount: BigDecimal,
val currency: Currency
) {
operator fun plus(other: Money): Money {
require(currency == other.currency) {
"Cannot add money of different currencies"
}
return Money(amount + other.amount, currency)
}
operator fun minus(other: Money): Money {
require(currency == other.currency) {
"Cannot subtract money of different currencies"
}
return Money(amount - other.amount, currency)
}
operator fun unaryMinus(): Money = Money(-amount, currency)
operator fun times(times: Int): Money =
Money(amount * times.toBigDecimal(), currency)
companion object {
fun eur(amount: String) =
Money(BigDecimal(amount), Currency.EUR)
}
}
Example solution in playground
import org.junit.Test
import java.math.BigDecimal
import kotlin.test.assertEquals
data class Money(
val amount: BigDecimal,
val currency: Currency
) {
operator fun plus(other: Money): Money {
require(currency == other.currency) {
"Cannot add money of different currencies"
}
return Money(amount + other.amount, currency)
}
operator fun minus(other: Money): Money {
require(currency == other.currency) {
"Cannot subtract money of different currencies"
}
return Money(amount - other.amount, currency)
}
operator fun unaryMinus(): Money = Money(-amount, currency)
operator fun times(times: Int): Money =
Money(amount * times.toBigDecimal(), currency)
companion object {
fun eur(amount: String) =
Money(BigDecimal(amount), Currency.EUR)
}
}
enum class Currency {
EUR, USD, GBP
}
fun main() {
val money1 = Money.eur("10.00")
val money2 = Money.eur("29.99")
println(money1 + money2) // Money(amount=39.99, currency=EUR)
println(money2 - money1) // Money(amount=19.99, currency=EUR)
println(-money1) // Money(amount=-10.00, currency=EUR)
println(money1 * 3) // Money(amount=30.00, currency=EUR)
}
class MoneyOperationsTest {
@Test
fun `Money can be added`() {
val money1 = Money.eur("10.00")
val money2 = Money.eur("29.99")
assertEquals(Money.eur("39.99"), money1 + money2)
}
@Test
fun `Money throws exception when adding different currencies`() {
for (currency in Currency.entries) {
for (otherCurrency in (Currency.entries - currency)) {
val money1 = Money(BigDecimal("10.00"), currency)
val money2 = Money(BigDecimal("29.99"), otherCurrency)
assertThrows<IllegalArgumentException> { money1 + money2 }
}
}
}
@Test
fun `Money can be subtracted`() {
val money1 = Money.eur("10.00")
val money2 = Money.eur("29.99")
assertEquals(Money.eur("19.99"), money2 - money1)
}
@Test
fun `Money throws exception when subtracting different currencies`() {
for (currency in Currency.entries) {
for (otherCurrency in (Currency.entries - currency)) {
val money1 = Money(BigDecimal("10.00"), currency)
val money2 = Money(BigDecimal("29.99"), otherCurrency)
assertThrows<IllegalArgumentException> { money1 - money2 }
}
}
}
@Test
fun `Money can be negated`() {
assertEquals(Money.eur("-10.00"), -Money.eur("10.00"))
assertEquals(Money.eur("-100.00"), -Money.eur("100.00"))
assertEquals(Money.eur("10.00"), -Money.eur("-10.00"))
assertEquals(Money.eur("-999.999"), -Money.eur("999.999"))
}
@Test
fun `Money can be multiplied by a number`() {
assertEquals(Money.eur("30.00"), Money.eur("10.00") * 3)
assertEquals(Money.eur("0.00"), Money.eur("10.00") * 0)
assertEquals(Money.eur("-30.00"), Money.eur("10.00") * -3)
}
}
inline fun <reified T: Throwable> assertThrows(operation: () -> Unit) {
val result = runCatching { operation() }
assert(result.isFailure) { "Operation has not failed with exception" }
val exception = result.exceptionOrNull()
assert(exception is T) { "Incorrect exception type, it should be ${T::class}, but it is $exception" }
}
