The most idiomatic way to perform conditional concatenation of strings in Scala

Question

I'm curious what would be the best way to build a String value via sequential appending of text chunks, if some of chunks dynamically depend on external conditions. The solution should be idiomatic for Scala without much speed and memory penalties.

For instance, how one could re-write the following Java method in Scala?

public String test(boolean b) {
    StringBuilder s = new StringBuilder();
    s.append("a").append(1);
    if (b) {
        s.append("b").append(2);
    }
    s.append("c").append(3);
    return s.toString();
}

Answer 1

Since Scala is both functional and imperative, the term idiomatic depends on which paradigm you prefer to follow. You've solved the problem following the imperative paradigm. Here's one of the ways you could do it functionally:

def test( b : Boolean ) =
  "a1" + 
  ( if( b ) "b2" else "" ) +
  "c3"

Answer 2

These days, idiomatic means string interpolation.

s"a1${if(b) "b2" else ""}c3"

You can even nest the string interpolation:

s"a1${if(b) s"$someMethod" else ""}"

Answer 3

What about making the different components of the string functions in their own right? They have to make a decision, which is responsibility enough for a function in my book.

def test(flag: Boolean) = {
  def a = "a1"
  def b = if (flag) "b2" else ""
  def c = "c3" 
  a + b + c
}

The added advantage of this is it clearly breaks apart the different components of the final string, while giving an overview of how they fit together at a high level, unencumbered by anything else, at the end.