Question

I was going through the wonderful book Programming in Scala when I came across a piece of code that just doesn’t make sense to me:

def above(that: Element): Element = {
    val this1 = this widen that.width
    val that1 = that widen this.width
    elem(this1.contents ++ that1.contents)
}

Note line 2 and 3:

val this1 = this widen that.width 

It seems like I should be able to replace this with:

val this1 = this.widen that.width

However, when I try to compile this change, it gives the following error:

error: ‘;’ expected but ‘.’ found.
val this1 = this.widen that.width
^

Why is this syntax unacceptable?

Answer 1

Line 2 uses the method widen as an operator, instead of using it as a method in the Java way:

val this1 = this.widen(that.width)

The error occurs because you’ve left out the parentheses, which you can only do when you use a method in operator notation. You can’t do this for example:

"a".+ "b" // error: ';' expected but string literal found.

Instead you should write

"a".+ ("b")

Actually you can do this with integers, but that’s beyond the scope of this question.

Read more:

• Chapter 5 section 3 of your book is about the operator notation, at least in the first edition, version 5
• A Tour of Scala: Operators