Scala precedence of implied dots and parentheses

Question

How is the following "parenthesized"?

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

Is it the same as

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

In other words, do implied dots (".") and parentheses have the same precedence as the real ones?

Is the first version the same as

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

score 4 · Accepted Answer · edited May 23 '17 at 12:27

4

Operators starting with letters have the lowest precedence. + has low precedence but higher than map or mkString. So

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

should be parsed as:

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

Think of it as:

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

edited May 23 '17 at 12:27

Community

answered Sep 27 '12 at 14:21

huynhjl

2

Technically speaking, assignment operators have even lower precedence so it's often used by DSLs. – Eugene Yokota Sep 27 '12 at 14:40

1 Answers1