ca-implicit-conversions.md

title	type	description	num	previous-page	next-page
Implicit Conversions	section	This page demonstrates how to implement Implicit Conversions in Scala 3.	67	ca-multiversal-equality	ca-summary

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
plus1("1")

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

Discussion

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] =
  java.lang.Integer.valueOf(_)