deanwampler

val f123a: (T1 | T2 | T3) => String = _ match
  case t1: T1 => "T1"
  case t2: T2 => "T2"
  case t3: T3 => "T3"

val f123b: (T1 => String) & (T2 => String) & (T3 => String) = f123a

val t123s: Seq[T1 | T2 | T3] = Seq(new T1 {}, new T2 {}, new T3 {})
t123s.map(f123a)
t123s.map(f123b)

deanwampler

// Covariance:

val t1s: Seq[T1] = Seq(new T1 {})
val t2s: Seq[T2] = Seq(new T2 {})
val t3s: Seq[T3] = Seq(new T3 {})
val t123s1: Seq[T1 | T2 | T3] = t1s
val t123s2: Seq[T1 | T2 | T3] = t2s
val t123s3: Seq[T1 | T2 | T3] = t3s

// Contravariance?

deanwampler

val t1: T1 = new T1 {}
val t2: T2 = new T2 {}
val t3: T3 = new T3 {}

val t123a: T1 | T2 | T3 = t1
val t123b: T1 | T2 | T3 = t2
val t123c: T1 | T2 | T3 = t3

deanwampler

// Adapted from "Programming Scala, Third Edition" (http://programming-scala.com)
// https://github.com/deanwampler/programming-scala-book-code-examples/blob/master/src/main/scala/progscala3/meta/Invariant.scala
import scala.quoted.*

object invariantMinInline:
  val ignore = false

  inline def apply[T](         // Use of "minimal" inlining. Does it still work?
      predicate: => Boolean,   // Now we need by-name parameters!
      message: => String = "")(

deanwampler

// Adapted from "Programming Scala, Third Edition" (http://programming-scala.com)
// https://github.com/deanwampler/programming-scala-book-code-examples/blob/master/src/main/scala/progscala3/meta/Invariant.scala
import scala.quoted.*

object invariantDisabled:
  inline val ignore = true

  inline def apply[T](
      inline predicate: Boolean, 
      inline message: String = "")(

deanwampler

// Adapted from "Programming Scala, Third Edition" (http://programming-scala.com)
// https://github.com/deanwampler/programming-scala-book-code-examples/blob/master/src/main/scala/progscala3/meta/Invariant.scala
import scala.quoted.*

object invariantEnabled:
  inline val ignore = false

  inline def apply[T](
      inline predicate: Boolean, 
      inline message: String = "")(

deanwampler

package progscala3.erased

import scala.language.experimental.erasedDefinitions

@main def Main() =
  // Use the +: methods to construct sequences.
  val nes1 = "one" +: EmptySeq
  val nes2 = "two" +: nes1
  val nes3 = "three" +: nes2

deanwampler

package progscala3.erased

import scala.annotation.implicitNotFound
import scala.language.experimental.erasedDefinitions

sealed trait Emptiness
final class Empty extends Emptiness
final class NotEmpty extends Emptiness

@implicitNotFound("The seq must be empty")

deanwampler

// Requires a snapshot or nightly build of Scala
val scala3 = "3.1.3-RC1-bin-SNAPSHOT"

lazy val root = project
  .in(file("."))
  .settings(
    name := "erased-feature-example",
    description := "An example of the experimental 'erased' feature.",
    version := "0.0.1",
    scalaVersion := scala3,

deanwampler

import scala.compiletime.ops.int.*

// Only allowed values are Min <= N <= Max.
type Bounded[MIN <: Int, MAX <: Int] <: Int = MAX match 
  case MIN => MIN
  case ? => MAX | Bounded[MIN,MAX-1]

val zero15: Bounded[1,5] = 0      // ERROR
val one15: Bounded[1,5] = 1
val two15: Bounded[1,5] = 2