Scala idioms

When do we know a language? In English, when we say a penny for your thoughts, we are using an idiom. We can express ourselves more succinctly and natively using these. Beating around the bush is another one. If we pick up enough of these and hurl them around at times, this will makes us fluent.

It is almost the same with programming languages. You see a construct time and again and make use of notable features of a specific programming language. Here is a sample of idioms from a few prominent languages.

For example, here is an idiomatic Scala way to sum up two lists of numbers:

scala> val d1 = List(1, 2, 3, 4, 5)
d1: List[Int] = List(1, 2, 3, 4, 5)

scala> val d2 = List(11, 22, 33, 44, 55)
d2: List[Int] = List(11, 22, 33, 44, 55)

scala> (d1, d2).zipped map (_ + _)
res0: List[Int] = List(12, 24, 36, 48, 60)

We could do this in a roundabout way; however, note that your Scala colleagues would quickly comprehend what is happening. Try the following command:

scala> (1 to 100).map( _ * 2 ).filter(x => x % 3 == 0 && x % 4 == 0 && x % 5 == 0)
res2: scala.collection.immutable.IndexedSeq[Int] = Vector(60, 120, 180)

For numbers from 1 to 100, we multiply each number by 2. We select those numbers that are divisible by 3, 4, and 5.

Here we are chaining method calls together. Each method returns a new value. The input is left unmodified. The intermediate values are threaded from call to call.

We could also write the preceding command as follows

scala> val l1 = 1 to 100
… // output elided
scala> val l2 = l1.map(_ * 2)
 … // output elided
scala> val l3 = l2.filter(x => x % 3 == 0 && x % 4 == 0 && x % 5 == 0)
l3: scala.collection.immutable.IndexedSeq[Int] = Vector(60, 120, 180)

However, the fluent API style is more idiomatic.

Note

You can learn more about fluent interfaces at http://www.martinfowler.com/bliki/FluentInterface.html.

People relate easily to idiomatic code. When we learn and use various Scala idioms, we will write code in the Scala way.