igstan

class Sup
class Sub(val element: Int) extends Sup

def test1[B >: Sub](a: Sub, b: B): B = if (a.element < 0) b else a
//                        ||
//                        || difference
//                        ||
//                        \/
def test2[B >: Sub](a: Sub)(b: B): B = if (a.element < 0) b else a

igstan

trait Fn[A] {
  def apply[B >: A](t: B): B
}

class Sup
class Sub extends Sup

def test[S >: Sub](a: Sub): Fn[S] =
  new Fn[S] {
    override def apply[B >: S](b: B): B = if (true) a else b

igstan

trait Fn[A,B] {
  // AA is contravariant; BB is covariant
  // Similar to Function1[-AA, +BB]
  def apply[AA >: A, BB <: B](t: AA): BB
}

class Sup
class Sub extends Sup

def test[S >: Sub](a: Sub): Fn[S,S] =

igstan

object Example {

  trait HttpParser[A] {
    // For the sake of simplicity, parse doesn't take any params.
    // Returning an Option is to reflect the fact that parse may
    // fail.
    def parse: Option[A]
  }

  trait HttpRenderer[B] {

igstan

object Example {

  trait HttpParser[A] {
    def parse: Option[A]
  }

  trait HttpRenderer[B] {
    def render(b: B): String
  }

igstan

igstan

// Dependency comes first when currying: OO-style constructors.
function foo(dependency) {
  return function (a) {
    return dependency(a);
  }
}

// Dependency comes last when currying: Reader Monad.
function foo(a) {
  return function (dependency) {

igstan

<?php

namespace acme;

function array_key_exists($key, $a) {
  if ($a instanceof \ArrayAccess) {
    return $a->offsetExists($key);
  } else {
    return \array_key_exists($key, $a);
  }

igstan

<?php

namespace acme;

function array_key_exists($key, $a) {
  if ($a instanceof \ArrayAccess) {
    return $a->offsetExists($key);
  } else {
    return \array_key_exists($key, $a);
  }

igstan

trait A {
  val count: Int
  val elements: Array[String] = new Array(count)
}

class C extends A {
  override val count = 10
}

val c = new C