Scala 3 — Book

Implicit Conversions


Implicit conversions are defined by given instances of the scala.Conversion class. For example, not accounting for possible conversion errors, this code defines an implicit conversion from String to Int:

given Conversion[String, Int] with
  def apply(s: String): Int = Integer.parseInt(s)

Using an alias this can be expressed more concisely as:

given Conversion[String, Int] = Integer.parseInt(_)

Using either of those conversions, you can now use a String in places where an Int is expected:

import scala.language.implicitConversions

// a method that expects an Int
def plus1(i: Int) = i + 1

// pass it a String that converts to an Int

Note the clause import scala.language.implicitConversions at the beginning, to enable implicit conversions in the file.


The Predef package contains “auto-boxing” conversions that map primitive number types to subclasses of java.lang.Number. For instance, the conversion from Int to java.lang.Integer can be defined as follows:

given int2Integer: Conversion[Int, java.lang.Integer] =

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