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def getSome(a: Int): Option[Int] = Some(a)

def getNone(a: Int): Option[Int] = None

def add(a: Int, b: Int): Int = a + b

val aOpt = getSome(1)

val bOpt = getSome(2)

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package org.example.ktz.blog


import cats.syntax.all._
import cats.instances.future._
import org.scalatest._

import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.duration._
import scala.concurrent.{Await, Future}

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import cats.data.Writer

def greetW(name: String, logged: Boolean): Writer[List[String], String] =
  Writer(List("Compose a greeting"), {
    val userName = if(logged) name else "User"
    s"Hello $userName"
  })

def isLoggedW(name: String): Writer[List[String], Boolean] =
  Writer(List("Checking if user is logged in"), name.length == 3)

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trait AuthService {
  def isLogged(name: String): Boolean
}

class AuthServiceChar3 extends AuthService{
  override def isLogged(name: String): Boolean = name.length == 3
}

class AuthServiceChar5 extends AuthService{
  override def isLogged(name: String): Boolean = name.length == 5

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class Person(val name: String, val age: Int, val weight: Int)

object Person {
  def apply(name: String, age: Int, weight: Int): Person = new Person(name, age, weight)

  def unapply(arg: Person): Option[(String, Int, Int)] =
    if(arg.age >= 20) Some(arg.name, arg.age, arg.weight)
    else None
}

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type List[+A] = scala.collection.immutable.List[A]

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val obj: Object = "Hello World!"

val listString: List[String] = List.empty
val listAny: List[Any] = listString

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package org.ktz.example.blog;

import java.util.ArrayList;
import java.util.List;

public class Variance {
    public static void main(String[] args) {
        String str = "";
        Object obj = str;