New Control Syntax
Scala 3 has a new "quiet" syntax for control expressions that does not rely on enclosing the condition in parentheses, and also allows to drop parentheses or braces around the generators of a
if x < 0 then "negative" else if x == 0 then "zero" else "positive" if x < 0 then -x else x while x >= 0 do x = f(x) for x <- xs if x > 0 yield x * x for x <- xs y <- ys do println(x + y) try body catch case ex: IOException => handle
The rules in detail are:
- The condition of an
if-expression can be written without enclosing parentheses if it is followed by a
- The condition of a
while-loop can be written without enclosing parentheses if it is followed by a
- The enumerators of a
for-expression can be written without enclosing parentheses or braces if they are followed by a
for-expression expresses a
catchcan be followed by a single case on the same line. If there are multiple cases, these have to appear within braces (just like in Scala 2) or an indented block.
The Scala 3 compiler can rewrite source code from old syntax to new syntax and back. When invoked with options
-rewrite -new-syntax it will rewrite from old to new syntax, dropping parentheses and braces in conditions and enumerators. When invoked with options
-rewrite -old-syntax it will rewrite in the reverse direction, inserting parentheses and braces as needed.
In this article