键入错误推断

Question

给出以下代码:

implicit class RichString(s: String) {
  def !![T](createMessage: Long => T) = ()
}
case class SomeClass(i: Int, s: String, id: Long)

为什么这样:

"some string" !! SomeClass(5, "test", _)

不编译,抛出以下错误:

Missing parameter type for expanded function ((x$1) => "some string".$bang$bang(SomeClass(5, "test", x$1)))
 "some string" !! SomeClass(5, "test", _)
                                       ^

Type mismatch;
 found   : cmd1.SomeClass
 required: Long => cmd1.SomeClass "some string" !! SomeClass(5, "test", _)

但所有这些都编译得很好:

val f = SomeClass(5, "test", _)
"some string" !! f

"some string" !! ( SomeClass(5, "test", _) )

"some string" !! { SomeClass(5, "test", _) }

PS:这"some string" !! SomeClass(5, "test", _: Long)也会导致类型不匹配.

Answer 1

正如消息所说,"some string" !! SomeClass(5, "test", _)扩展为x => "some string" !! SomeClass(5, "test", x),而不是 "some string" !! { x => SomeClass(5, "test", x) }.所以!!没有收到函数,它收到一个SomeClass,不编译.