是否可以在Scala中强制命名参数？

Question

在某些方法中，我想强制命名参数。原因是未指定参数顺序的自动生成代码（并将保持这种方式）。

我能得到的最接近的是

private val _forceNamed: Object = new Object()

def doSomething(forceNamed: Object = _forceNamed, arg1: String, arg2: String, ...): Unit = {
  if (forceNamed != _forceNamed) {
    throw Exception(something)
  }

  // actually do stuff
}

但是，这只会在运行时失败，而在编译时失败会更好。

Answer 1

如果你想堵住能够传入的漏洞null，可以使用值类作为守卫。

scala> :paste
// Entering paste mode (ctrl-D to finish)

class Foo {
   import Foo._
   def foo(x: Bar = bar, a: String, b: String) = println(a + b)
}

object Foo {
  private[Foo] class Bar(val i: Int) extends AnyVal
  private val bar = new Bar(42)
}

// Exiting paste mode, now interpreting.

defined class Foo
defined object Foo

scala> val f = new Foo
f: Foo = Foo@4a4f9c58

scala> f.foo(null, "", "")
<console>:13: error: type mismatch;
 found   : Null(null)
 required: Foo.Bar
       f.foo(null, "", "")
             ^