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Scala for Backend Engineering & Functional Programming · Lesson

s, f and raw Interpolators

Embed values in strings.

s, f and raw Interpolators is a free Scala for Backend Engineering & Functional Programming lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Scala for Backend Engineering & Functional Programming learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

What Is Interpolation?

String interpolation lets you embed values directly inside a string literal.

Instead of joining pieces with +, you put a prefix letter before the quotes and reference variables inside. Scala has three built-in interpolators: s, f, and raw.

val name = "Ada"
println(s"Hello, $name!")

The s Interpolator

The s interpolator is the most common. Put s before the opening quote, then use $variable to insert a value.

It reads more clearly than concatenation with +.

val count = 3
println(s"You have $count messages")

Expressions with Braces

For anything more than a simple variable, wrap the expression in ${ }.

This lets you do arithmetic or call methods right inside the string.

val a = 4
val b = 5
println(s"Sum is ${a + b}")
println(s"Upper: ${"hi".toUpperCase}")

A Runnable s Example

Here is a complete program using the s interpolator to build a greeting.

Notice how the variables are inserted neatly into the sentence.

object Main extends App {
  val user = "Sam"
  val items = 2
  println(s"Hi $user, you bought $items items.")
}

Escaping a Dollar Sign

Inside an interpolated string, $ has special meaning. To print a literal dollar sign, write $$.

This is useful when formatting prices or currency.

val price = 9
println(s"Total: $$$price")

The f Interpolator

The f interpolator adds printf-style formatting. After a variable, add a format specifier like %d for integers or %s for strings.

It is great for controlling number precision and alignment.

val n = 42
println(f"Value: $n%d")
val label = "Pi"
println(f"$label%s")

Formatting Decimals

Use %f with a precision to control decimal places. For example %.2f shows two digits after the point.

This is ideal for money or measurements.

val pi = 3.14159
println(f"Pi is $pi%.2f")
val ratio = 0.5
println(f"Ratio: $ratio%.1f")

Width and Padding with f

The f interpolator can also pad numbers to a width. %5d right-aligns an integer in a field five characters wide.

This helps line up columns of output.

val x = 7
println(f"[$x%5d]")
println(f"[$x%-5d]")

The raw Interpolator

The raw interpolator works like s but does not process escape sequences.

So \n stays as the two characters backslash and n, instead of becoming a new line.

println(raw"Path: C:\new\test")
println(s"Path: C:\new\test")

Choosing the Right One

Use s for everyday value insertion. Use f when you need number formatting. Use raw when you want backslashes kept literally, like file paths or regex.

All three still support $variable and ${expression}.

val v = 1.0
println(s"s: $v")
println(f"f: $v%.2f")
println(raw"raw: $v\n")

Multiple Values Together

You can combine many variables and expressions in one interpolated string.

This keeps output code compact and easy to read compared to long chains of +.

object Main extends App {
  val item = "Coffee"
  val qty = 2
  val cost = 4.5
  println(f"$qty x $item = $$${qty * cost}%.2f")
}

Quick Check

Which interpolator keeps escape sequences literal?

Recap

You learned Scala's three interpolators. s inserts values with $var and ${expr}.

f adds printf-style formatting like %.2f and %5d. raw behaves like s but keeps escape sequences literal. Use $$ to print a real dollar sign.

Frequently asked questions

Is the “s, f and raw Interpolators” lesson free?

Yes — the full text of “s, f and raw Interpolators” is free to read here on the web, and the Scala for Backend Engineering & Functional Programming course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Scala for Backend Engineering & Functional Programming course, upgrade to CoddyKit PRO.

What will I learn in “s, f and raw Interpolators”?

Embed values in strings. You practise Scala for Backend Engineering & Functional Programming with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Scala for Backend Engineering & Functional Programming?

No prior experience is required. Scala for Backend Engineering & Functional Programming on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “s, f and raw Interpolators” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Scala for Backend Engineering & Functional Programming lesson?

Yes. Every Scala for Backend Engineering & Functional Programming lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. String Basics
  2. s, f and raw Interpolators
  3. Common String Methods
  4. Multiline Strings
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