When to use parenthesis in Scala infix notation

Question

When programming in Scala, I do more and more functional stuff. However, when using infix notation it is hard to tell when you need parenthesis and when you don\'t.

Answer 1

Here's a simple rule: never used postfix operators. If you do, put the whole expression ending with the postfix operator inside parenthesis.

In fact, starting with Scala 2.10.0, doing that will generate a warning by default.

For good measure, you might want to move the postfix operator out, and use dot notation for it. For example:

(fromFile(file)).mkString map caesar(k)_

Or, even more simply,

fromFile(file).mkString map caesar(k)_

On the other hand, pay attention to the methods where you can supply an empty parenthesis to turn them into infix:

fromFile(file) mkString () map caesar(k)_