隐含点和括号的 Scala 优先级

Question

下面的“括号”是怎么写的？

val words = List("foo", "bar", "baz")
val phrase = "These are upper case: " + words map { _.toUpperCase } mkString ", "

是不是一样

val words = List("foo", "bar", "baz")
val phrase = "These are upper case: " + words.map(_.toUpperCase).mkString(", ")

换句话说，隐含的点(“.”)和括号的优先级是否与真实的相同？

第一个版本是否相同

val words = List("foo", "bar", "baz")
val phrase =
  "These are upper case: " + (words map { _.toUpperCase } mkString ", ")

Answer 1

以字母开头的运算符具有最低的优先级。 + 的优先级较低，但高于 map 或 mkString。所以

"These are upper case: " + words map { _.toUpperCase } mkString ", "

应该解析为:

(("These are upper case: " + words).map{ _.toUpperCase }).mkString(", ")

把它想象成:

v1 + v2 map v3 mkString v4
((v1 + v2) map v3) mkString v4

有关更多信息，请参阅我的其他答案:When to use parenthesis in Scala infix notation