我想通过与Haskell的newtype比较，我理解了Scala 2.10的新“值类”功能：

trait BoundedValue[+This] extends Any { this: This =>

def upperBound: This

def lowerBound: This

}

class Probability @throws(classOf[IllegalArgumentException]) (v: Double) extends AnyVal with BoundedValue[Probability] {

val value: Double = if ((v >= 0.0) && (v <= 1.0)) v else throw new IllegalArgumentException((v.toString) + "is not within the range [0.0, 1.0]")

override val upperBound: Probability = new Probability(0.0)

override val lowerBound: Probability = new Probability(1.0)

// Implement probability arithmetic here;

// will be represented by Double at runtime.

}我的问题是，对于使用声明它的Scala包的Java代码，值类如何显示？值类是从Java方面作为引用类出现的，还是被完全擦除(并因此显示为它所包装的类型)？换句话说，当Java在源代码级别上涉及时，类型安全是否是值类？

编辑

根据SIP-15文档(在Daniel的回答中链接)，上面的代码不会被编译，因为值类不允许有任何初始化逻辑，因为v必须显式为val，或者Probability必须有unbox方法以及对应的box方法，因为值类必须只有一个字段。正确的代码是：

trait BoundedValue[This <: boundedvalue extends any this: this="">

def upperBound: This

def lowerBound: This

}

class Probability private[Probability] (value: Double) extends AnyVal with BoundedValue[Probability] {

@inline override def upperBound: Probability = new Probability(0.0)

@inline override def lowerBound: Probability = new Probability(1.0)

@inline def unbox: Double = value

// Implement probability arithmetic here;

// will be represented by Double at runtime (mostly).

}

object Probability {

@throws(classOf[IllegalArgumentException])

def box(v: Double): Probability = if ((v >= 0.0) && (v <= 1.0)) new Probability(v) else throw new IllegalArgumentException((v.toString) + "is not within the range [0.0, 1.0]")

}然而，问题本身仍然有效。