erokhins

Allow out type parameter to safely occur in in position

• Type: Design proposal
• Author: Viacheslav Makarov
• Status: Draft

Summary

Reduce the need in @UnsafeVariance. Allow covariant types to have non-private methods with non-covariant signature. To protect class' covariance, out-project signatures

erokhins

// FILE: 1.kt
package p3

class A {
    fun<T> inTransaction(block: (tran: String) -> T): T {
        println("Function 1")
        return block("")
    }

    fun inTransaction(block: (tran: String) -> Unit) {

erokhins

// FILE: 1.kt
package p3

class A {
    fun <T> test(a: List<T>): Int {
        println("Function 1")
        return 1
    }
    fun test(b: List<Int>) {
        println("Function 2")

erokhins

Code fragment:

fun test() = 1 // comment

Kotlin code fragment:

fun test2() = 2 // comment

erokhins

fun bar(s: List<String>) {}

fun test() {
    bar(listOf().filter { false })
}

erokhins

\documentclass[10pt]{article}
\usepackage[utf8]{inputenc}
\usepackage[english,russian]{babel}
\inputencoding{utf8}
\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{amssymb}

\newcommand{\Expect}{\mathbb E}
\newcommand{\PRob}{\mathbb P}

erokhins

trait Inv<T> {
    var t: T
}

fun <T> some(t: Inv<T>): Inv<Inv<T>> {
    return object : Inv<Inv<T>> {
        override var t: Inv<T>
            get() = t
            set(value: Inv<T>) {
                t.t = value.t

erokhins

public class Test {
    private static class A {
        private int bar;
        private A() {
            bar = 3;
            System.out.println(getBar());
        }

        public int getBar() {
            return bar;

erokhins

open class A {
  open val bar: Int
  {
    bar = 3
    println(bar)
  }
}

class B : A() {
  override val bar = 4

erokhins

open class A() {
    open fun bar(t: Int = 1) = t
}

class B: A() {
    override fun bar(t: Int): Int {
        return super.bar()
    }
}