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miles@tarski:~% cs launch scala3-repl   
scala> trait A                                                                                                                              
     | trait B
     | type M[X] = X match
     |   case A => Int
     |   case B => String
     | 
// defined trait A
// defined trait B

milessabin

import cats.{Applicative, Monad}
import cats.implicits._

abstract class Foo[+M[_[_]], F[_]](implicit val M: M[F])
trait Bar[F[_]] extends Foo[Applicative, F] { def bar = Applicative[F] }
trait Baz[F[_]] extends Foo[Monad, F] { def baz = Monad[F] }

class User[F[_]: Monad] extends Bar[F] with Baz[F]

object Test {

milessabin

import cats.{Applicative, Monad}
import cats.implicits._

abstract class Foo[+M[_[_]], F[_]](implicit val M: M[F])
trait Bar[F[_]] extends Foo[Applicative, F] { def bar = Applicative[F] }
trait Baz[F[_]] extends Foo[Monad, F] { def baz = Monad[F] }

class User[F[_]: Monad] extends Bar[F] with Baz[F]

object Test {

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/*
 * Copyright (c) 2019 Miles Sabin 
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software

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def tupleType(tpes: List[Type]): Type = {
  val PairType = typeOf[_ *: _] match {
    case Type.IsAppliedType(tp) => tp.tycon
  }

  @tailrec
  def nestedPairs(tpes: List[Type], acc: Type): Type = tpes match {
    case Nil => acc
    case hd :: tail => nestedPairs(tail, Type.AppliedType(PairType, List(hd, acc)))
  }

milessabin

object Utils {
  type Id[t] = t
  type Const[c] = [t] => c
}

import Utils._

class Instances[F[_[_]], T[_]]

trait Functor[F[_]]

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Implicit Function Types

References

• Scala Contributors thread.
• Dotty documentation page
• Pre-SIP: ThisFunction
• DelayedInit/onCreate thread.
• Scope injection thread.

milessabin

// local/localtests/test/localtests/LocalTests.scala
package localtests

import java.nio.file._
import java.util.stream.{ Stream => JStream }

import org.junit.{ AfterClass, Test }

import scala.collection.JavaConverters._
import scala.concurrent.duration._

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References

• Scala Contributors thread.

• Dotty issue: Weak eta-expansion.

• Martin's comment on the issue above.

Comments

milessabin

miles@tarski:perf_tester (topic/miles-byname-implicits)% java -jar target/scala-2.12/perf_tester-assembly-0.1.jar -s /home/miles/projects/scala -r results -a corpus/scala-library -c miles-byname-implicits --user miles -i 50 -p 3
Output logging to /home/miles/projects/perf_tester/results/miles/miles-byname-implicits

ALL
                 Run Name       Cycle   samples            Wall time (ms)              All Wall time (ms)                         CPU(ms)                  Idle time (ms)                  Allocated(MBs)
                   pre-pr          1      50    9,332.00 [-10.92% +203.33%]     9,332.00 [-10.92% +203.33%]     9,188.06 [-10.64% +196.26%]            0.00 [ NaN%  NaN%]        2,743.61 [-0.38% +6.58%]
                   pre-pr          2      50    9,088.94 [-10.42% +192.67%]     9,088.94 [-10.42% +192.67%]     8,959.18 [-10.03% +185.47%]            0.00 [ NaN%  NaN%]        2,745.65 [-0.51% +6.81%]
                   pre-pr          3      50    9,176.00 [-9.87% +199.00%]      9,176.00 [-9.87%