Scala for Backend Engineering & Functional Programming · Lesson

Implicit Conversions

Use with care.

What is an implicit conversion?

An implicit conversion automatically transforms a value of one type into another when the compiler needs it. It can make APIs more convenient, but it must be used with care because it hides what is happening.

object Main {
  import scala.language.implicitConversions
  implicit def intToString(x: Int): String = s"number-$x"
  def main(args: Array[String]): Unit = {
    val s: String = 42
    println(s)
  }
}

How the compiler uses them

When a value's type does not match what is expected, the compiler searches for an implicit conversion that fixes the mismatch and inserts it silently.

object Main {
  import scala.language.implicitConversions
  implicit def doubleToInt(d: Double): Int = d.toInt
  def addTen(x: Int): Int = x + 10
  def main(args: Array[String]): Unit = {
    println(addTen(3.9))
  }
}

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