Scala:在类型别名不匹配时强制编译错误

Question

在分配共享相同基础类型的不同类型别名时，有没有办法获得编译时错误(或至少警告)？

换句话说，假设我有这个代码:

type Address = String
type City = String

def foo(x:Address) = ...

如果我这样做，我想获得编译时错误/警告:

val city: City = "Dublin"
foo(city)

据我所知，编译器允许它，因为它们是相同的底层类型。

Answer 1

据我所知，不可能获得您为类型别名寻求的这种“类型安全”。但是，还有一种替代类型别名可用于您的需要:Value Classes .基本上，值类可以在不分配新对象的情况下为您提供类型。请注意，对于类型别名没有的值类有一些限制。
引用 Scala 文档:

Correctness

Another use case for value classes is to get the type safety of a data type without the runtime allocation overhead. For example, a fragment of a data type that represents a distance might look like:

  class Meter(val value: Double) extends AnyVal {
    def +(m: Meter): Meter = new Meter(value + m.value)
  }

Code that adds two distances, such as

  val x = new Meter(3.4)
  val y = new Meter(4.3)
  val z = x + y

will not actually allocate any Meter instances, but will only use primitive doubles at runtime.