+ Kotlin 中的运算符给出"Unresolved reference. None of the following candidates is applicable because of rec

Question

我通过在exercism.com上做练习来学习Kotlin。我现在正在研究三角形。代码中有以下我试图通过的测试:

class TriangleTest {
@Test(expected = IllegalArgumentException::class)
fun `triangle inequality violation - last is greater then sum of others `() {
Triangle(1, 1, 3)
}
}

我的解决方案:

class Triangle<out T : Number>(private val a: T, private val b: T, private val c: T) {
init {
// ...
if (a + b <= c) {
throw IllegalArgumentException()
}
}
}

IntelliJ突出显示+红色并给出以下错误:

Unresolved reference. None of the following candidates is applicable because of receiver type mismatch:
public inline operator fun BigDecimal.plus(other: BigDecimal): BigDecimal defined in kotlin
public inline operator fun BigInteger.plus(other: BigInteger): BigInteger defined in kotlin
...

对于来自数组和集合类型的其他plus()方法，这种情况持续了大约100行。

为什么我不能在这里的init块中添加两个数字?

Answer 1

这是因为Kotlin没有为添加两个Number提供plus过载。一种方法是将Number转换为Double，然后对它们执行操作。此外，Kotlin还为此类验证提供了一个方便的require函数。

class Triangle(val a: Number, val b: Number, val c: Number) {
init {
val (x, y, z) = listOf(a.toDouble(), b.toDouble(), c.toDouble())
require(x + y > z)
}
}