Indentation

Each level of indentation is 2 spaces. Tabs are not used. Thus, instead of indenting like this:

// wrong!
class Foo {
    def fourspaces = {
        val x = 4
        ..
    }
}

You should indent like this:

// right!
class Foo {
  def twospaces = {
    val x = 2
    ..
  }
}

The Scala language encourages a startling amount of nested scopes and logical blocks (function values and such). Do yourself a favor and don’t penalize yourself syntactically for opening up a new block. Coming from Java, this style does take a bit of getting used to, but it is well worth the effort.

Line Wrapping

There are times when a single expression reaches a length where it becomes unreadable to keep it confined to a single line (usually that length is anywhere above 80 characters). In such cases, the preferred approach is to simply split the expression up into multiple expressions by assigning intermediate results to values. However, this is not always a practical solution.

When it is absolutely necessary to wrap an expression across more than one line, each successive line should be indented two spaces from the first. Also remember that Scala requires each “wrap line” to either have an unclosed parenthetical or to end with an infix method in which the right parameter is not given:

val result = 1 + 2 + 3 + 4 + 5 + 6 +
  7 + 8 + 9 + 10 + 11 + 12 + 13 + 14 +
  15 + 16 + 17 + 18 + 19 + 20

Without this trailing method, Scala will infer a semi-colon at the end of a line which was intended to wrap, throwing off the compilation sometimes without even so much as a warning.

Methods with Numerous Arguments

When calling a method which takes numerous arguments (in the range of five or more), it is often necessary to wrap the method invocation onto multiple lines. In such cases, put each argument on a line by itself, indented two spaces from the current indent level:

foo(
  someVeryLongFieldName,
  andAnotherVeryLongFieldName,
  "this is a string",
  3.1415)

This way, all parameters line up, but you don’t need to re-align them if you change the name of the method later on.

Great care should be taken to avoid these sorts of invocations well into the length of the line. More specifically, such an invocation should be avoided when each parameter would have to be indented more than 50 spaces to achieve alignment. In such cases, the invocation itself should be moved to the next line and indented two spaces:

// right!
val myLongFieldNameWithNoRealPoint =
  foo(
    someVeryLongFieldName,
    andAnotherVeryLongFieldName,
    "this is a string",
    3.1415)

// wrong!
val myLongFieldNameWithNoRealPoint = foo(someVeryLongFieldName,
                                         andAnotherVeryLongFieldName,
                                         "this is a string",
                                         3.1415)

Better yet, just try to avoid any method which takes more than two or three parameters!