scala - 如何转换 "pimp"方法来接受元组？

Question

val t = (0f, 0f)

def g(x: Float, y: Float): Unit = {
  println(s"g($x, $y)")
}

g(1, 1)
(g _).tupled(t) // working

implicit class Pimps[A <: Object](a: A) {
  def f(x: Float, y: Float): A = {
    println(s"f($x, $y)")
    a
  }
}

"".f(1, 1)
("".f _).tupled(t) // not working

这种行为对我来说似乎非常令人困惑和不一致。我得到:

a.sc:18: missing argument list for method f in class Pimps
Unapplied methods are only converted to functions when a function type is expected.
You can make this conversion explicit by writing `f _` or `f(_,_)` instead of `f`.
val res_6 = ("".f _).tupled(t) // not working
                ^
Compilation Failed

为什么它在第一种情况下有效，而在第二种情况下不起作用？

如何修复“不工作”行，以便可以使用元组参数调用函数而不解构元组(意味着不使用 ._1、. _2 或匹配)？

Answer 1

编辑:

这看起来像SI-8299

---

这对我来说就像一个错误。如果我们稍微简化一下并显式实例化隐式类，则可以执行以下操作:

implicit class Pimps(a: String) {
  def f(x: Float, y: Float): String = a
}

(new Pimps("").f _).tupled // works

查看 ("".f _).tupled 的 -Ytyper-debug 输出:

|-- ("".f: (() => <empty>)).tupled : pt=Unit EXPRmode (site: method main in Implicit)
|    |    |    |    |-- ("".f: (() => <empty>)) EXPRmode-POLYmode-QUALmode (site: method main in Implicit)
|    |    |    |    |    |-- "" EXPRmode-POLYmode-QUALmode (site: method main in Implicit)
|    |    |    |    |    |    \-> String("")
|    |    |    |    |    [search #1] start `""`, searching for adaptation to pt=String("") => ?{def f: ?} (silent: method main in Implicit) implicits disabled
|    |    |    |    |    [search #1] considering Pimps
|    |    |    |    |    |-- Pimps BYVALmode-EXPRmode-FUNmode-POLYmode (silent: method main in Implicit) implicits disabled
|    |    |    |    |    |    \-> (a: String)Pimps
|    |    |    |    |    [search #1] success inferred value of type String("") => ?{def f: ?} is SearchResult(Pimps, )
|    |    |    |    |    |-- (a: String)Pimps EXPRmode-POLYmode-QUALmode (silent: method main in Implicit)
|    |    |    |    |    |    \-> Pimps
|    |    |    |    |    |-- Pimps("").f EXPRmode-POLYmode-QUALmode (site: method main in Implicit)
Implicit.scala:21: error: missing argument list for method f in class Pimps
Unapplied methods are only converted to functions when a function type is expected.
You can make this conversion explicit by writing `f _` or `f(_,_)` instead of `f`.
    ("".f _).tupled

虽然编译器正确解析了隐式类，但随后到达方法定义并失败。

您可以通过使用类型归属来解决此问题:

("".f: (Float, Float) => String).tupled

或者通过将函数绑定(bind)到键入的值:

val func: (Float, Float) => String = "".f
func.tupled