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15: Coding Scala Way – Scala concurrency & closure vs function definition

This post not only covers “onSuccess” method on a “Future”, but also clarifies the difference between executing a closure and a function definition. Is anything wrong with the following Scala concurrency code?


import scala.concurrent.ExecutionContext.Implicits.global //thread pool execution context
import scala.concurrent.{Await, Future}
import scala.actors.threadpool.AtomicInteger
import scala.concurrent.duration._ // 5 seconds

object SimpleFuture extends App {
  
  val counter = new AtomicInteger
  
  //can succeed or fail
  val futureInc = Future {
    Thread.sleep(2000) // 2000ms processing time
    println("Incrementing .....")
    counter.incrementAndGet() 
  }
  
  val f1: Future[Int] = futureInc
  val f2: Future[Int] = futureInc
  
  f1.onSuccess {
    
    case val1 => {
      
      println("val1 = " + val1)
      
      f2.onSuccess {
       
        case val2 => 
          println("val2 = " + val2)
          println("Sum of generated numbers = " + (val1 + val2))
      }
    }
  }
  
 Thread.sleep(5000)
  
}

import scala.concurrent.ExecutionContext.Implicits.global //thread pool execution context

import scala.concurrent.{Await, Future}

import scala.actors.threadpool.AtomicInteger

import scala.concurrent.duration._ // 5 seconds

object SimpleFuture extends App {

val counter = new AtomicInteger

//can succeed or fail

val futureInc = Future {

Thread.sleep(2000) // 2000ms processing time

println("Incrementing .....")

counter.incrementAndGet()

}

val f1: Future[Int] = futureInc

val f2: Future[Int] = futureInc

f1.onSuccess {

case val1 => {

println("val1 = " + val1)

f2.onSuccess {

case val2 =>

println("val2 = " + val2)

println("Sum of generated numbers = " + (val1 + val2))

}

Thread.sleep(5000)

}

Output:


Incrementing .....
val1 = 1
val2 = 1
Sum of generated numbers = 2

Incrementing .....

val1 = 1

val2 = 1

Sum of generated numbers = 2

“ … Read more ›...

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15: Q88 – Q92 Scala Functors Interview Q&As

This extends Category Theory With Scala Interview Q&As. Q88. What do you understand by the terms functors, monads, and applicatives ? A88. Functors, Monads, and Applicatives are concepts or patterns that abstract complexities in computations, and are NOT traits or classes. … Read more ›...

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15B: Scala Functors Interview Q&As by example

Prerequisite: Scala values, proper types, first order types & higher kinded types. Q. Is it possible to further abstract the below code?


package com.functor

import scala.util.Try
import scala.util.Success

object FunctorExample extends App {

  def timesByTwoList(input: List[Int]): List[Int] = input.map(_ * 2)

  def timesByTwoOption(input: Option[Int]): Option[Int] = input.map(_ * 2)
  
  def timesByTwoTry(input: Try[Int]): Try[Int] = input.map(_ * 2)
  
  println(timesByTwoList(List(1,2,3)));
  println(timesByTwoOption(Some(4)));
  println(timesByTwoTry(Success(5)));

}

package com.functor

import scala.util.Try

import scala.util.Success

object FunctorExample extends App {

def timesByTwoList(input: List[Int]): List[Int] = input.map(_ * 2)

def timesByTwoOption(input: Option[Int]): Option[Int] = input.map(_ * 2)

def timesByTwoTry(input: Try[Int]): Try[Int] = input.map(_ * 2)

println(timesByTwoList(List(1,2,3)));

println(timesByTwoOption(Some(4)));

println(timesByTwoTry(Success(5)));

}

Output:


List(2, 4, 6)
Some(8)
Success(10)

List(2, 4, 6)

Some(8)

Success(10)

A. Why have different timesByTwoXXX functions for each container type like List, … Read more ›...

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16: Coding Scala Way – Scala concurrency styles

This extends Scala concurrency & closure vs function definition. This post looks at Scala concurrency styles – blocking & non-blocking. onComplete – non-blocking


import scala.concurrent.ExecutionContext.Implicits.global //thread pool execution context
import scala.concurrent.{ Await, Future }
import scala.actors.threadpool.AtomicInteger
import scala.concurrent.duration._ // 5 seconds
import scala.util.{ Failure, Success }

object SimpleFuture extends App {

  val counter = new AtomicInteger

  //can succeed or fail
  def futureInc() = Future {
    Thread.sleep(2000);
    println("Incrementing .....")
    counter.incrementAndGet()
  }

  val f1 = futureInc  
  val f2 = futureInc   

  f1.onComplete {
    case Success(val1) => {
      println("val1 = " + val1)
      f2.onComplete {
        case Success(val2) => {
          println("val1 = " + val2)
          println("Sum of generated numbers = " + (val1 + val2))
        }

        case Failure(e) => e.printStackTrace

      }
    }
    case Failure(e) => e.printStackTrace

  }

  println("I am not blocked .......");
  println("Other operations .......");

  Thread.sleep(5000) //

}

import scala.concurrent.ExecutionContext.Implicits.global //thread pool execution context

import scala.concurrent.{ Await, Future }

import scala.actors.threadpool.AtomicInteger

import scala.concurrent.duration._ // 5 seconds

import scala.util.{ Failure, Success }

object SimpleFuture extends App {

val counter = new AtomicInteger

//can succeed or fail

def futureInc() = Future {

Thread.sleep(2000);

println("Incrementing .....")

counter.incrementAndGet()

}

val f1 = futureInc

val f2 = futureInc

f1.onComplete {

case Success(val1) => {

println("val1 = " + val1)

f2.onComplete {

case Success(val2) => {

println("val1 = " + val2)

println("Sum of generated numbers = " + (val1 + val2))

}

case Failure(e) => e.printStackTrace

}

case Failure(e) => e.printStackTrace

}

println("I am not blocked .......");

println("Other operations .......");

Thread.sleep(5000) //

}

Output:


I am not blocked .......
Other operations .......
Incrementing .....
Incrementing .....
val1 = 2
val1 = 1
Sum of generated numbers = 3

I am not blocked .......

Other operations .......

Incrementing .....

val1 = 2

val1 = 1

Sum of generated numbers = 3

onSuccess – non-blocking The above “onComplete” call is highly nested. “ … Read more ›...

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16: Q93 – Q98 Scala monads interview Q&As

This extends Scala Functors Interview Q&As. You need to remember the following.


Applying function of signature:
-----------------------------
"T => R"                           to return  "C[T] => C[R]"    is a  Functor
"T => C[R]"                        to return  "C[T] => C[R]"    is a  Monad
"C[T => R]"                        to return  "C[T] => C[R]"    is an Applicative

Applying function of signature:

-----------------------------

"T => R" to return "C[T] => C[R]" is a Functor

"T => C[R]" to return "C[T] => C[R]" is a Monad

"C[T => R]" to return "C[T] => C[R]" is an Applicative

Where T & R are raw types like String, Int, Employee, etc, and C is a container or wrapper type like List, Option, Future, List, etc. So, T =R could be a type abstraction for Int =Int,...

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16B: Scala Monoids, Functors & Monads interview Q&As

Scala Monoids, Functors & Monads interview questions are very popular & form the basis for the functional programming. Q01. Given the below code, is it possible to implement the map(..) method with flatMap(…) within the Monad trait?

package com.monad

object MyMonad extends App {

  trait Monoid[A] {
    def identity: A

    def combine(a: A, b: A): A
  }

  trait Functor[F[_]] {
    def map[A, B](a: F[A])(f: A => B): F[B]
  }

  trait Monad[M[_]] extends Functor[M] /* with Monoid[_ => M[_]] */ {
    def pure[A](a: A): M[A]

    def flatMap[A, B](a: M[A])(f: A => M[B]): M[B]

  }
}

package com.monad

object MyMonad extends App {

trait Monoid[A] {

def identity: A

def combine(a: A, b: A): A

}

trait Functor[F[_]] {

def map[A, B](a: F[A])(f: A => B): F[B]

}

trait Monad[M[_]] extends Functor[M] /* with Monoid[_ => M[_]] */ {

def pure[A](a: A): M[A]

def flatMap[A, B](a: M[A])(f: A => M[B]): M[B]

}

A01. Yes. … Read more ›...

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17: Coding Scala Way – What is wrong with this code?

Q. What is wrong with the below code? How will you fix it?


package com.myapp

object Test extends App {

  val map = Map (
     "1" -> "2015",
     "2" -> "2016",
     "3" -> "2017"
  )

  def isCorrectYearById(id: String, year: String) : Boolean = {
    map.get(id) == year
  }

  println(isCorrectYearById("2", "2016"))
}

package com.myapp

object Test extends App {

val map = Map (

"1" -> "2015",

"2" -> "2016",

"3" -> "2017"

)

def isCorrectYearById(id: String, year: String) : Boolean = {

map.get(id) == year

}

println(isCorrectYearById("2", "2016"))

}

A. The above code will always return “false”. Why? Because map.get(id) returns Some(2016), which is not == to the String value of “2016”. The “==”

…

17: Q99 – Q103 Scala applicative functors interview Q&As

This extends Scala Functors Interview Q&As & Scala monads interview Q&As. You need to remember the following.


"T => R"      to return  "C[T] => C[R]"    is a  Functor
"T => C[R]"   to return  "C[T] => C[R]"    is a  Monad
"C[T => R]"   to return  "C[T] => C[R]"    is an Applicative Functor

"T => R" to return "C[T] => C[R]" is a Functor

"T => C[R]" to return "C[T] => C[R]" is a Monad

"C[T => R]" to return "C[T] => C[R]" is an Applicative Functor


"Int => Boolean"                to return "MyContainer[Int] => MyContainer[Boolean]"   is a  Functor
"Int => MyContainer[Boolean]"   to return "MyContainer[Int] => MyContainer[Boolean]"   is a  Monad
"MyContainer[Int => Boolean]"   to return "MyContainer[Int] => MyContainer[Boolean]"   is an Applicative Functor

"Int => Boolean" to return "MyContainer[Int] => MyContainer[Boolean]" is a Functor

"Int => MyContainer[Boolean]" to return "MyContainer[Int] => MyContainer[Boolean]" is a Monad

"MyContainer[Int => Boolean]" to return "MyContainer[Int] => MyContainer[Boolean]" is an Applicative Functor

Q99. Why do you need an applicative functor? A99. The “map” method in the functor works with a single input argument as explained in the Scala functors interview Q&As. … Read...

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18: Q104 – Q108 Scala typeclass pattern for decoupling with polymorphism

Q104. What is the importance of “typeclass” pattern in Scala? A104. Typeclass pattern is to achieve decoupling via adhoc polymorphism. Polymorphism separates interfaces from implementations, to decouple what from how. Polymorphism improves code readability with better code organization. … Read more ›...

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19: Q109 – Q113 Scala ADT (Algebraic Data Types) Interview Q&As

Q109 How do you model data in functional programming (i.e. FP)? A109 Using ADT (i.e. Algebraic Data Types), you can model data with logical ORs and logical ANDs. “OR” is also known as the “Sum” … Read more ›...

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20: Q114 – Q120 Scala fold vs reduce Q&As

fold, map, and flatMap are key functional programming functions. These functions are used in three contexts: collections (E.g. List, Sequence, Array, Map, etc), Options, and Futures. Let’s look at the function “fold” here. Q114 What does fold & … Read more ›...

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21: Q121 – Q124 Scala Extractor Interview Q&As

Q121 What is an extractor object in Scala? A121 An extractor object is an object with an unapply method. The apply method is like a constructor which takes arguments and creates an object, the unapply takes an object and tries to give back the arguments. … Read more ›...

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22: What are the uses of underscore i.e _ in Scala?

The underscore (_) is one of the symbols used very widely in Scala. It is used as a Wild card, Place holder, Except, Ignore etc. Module Import Used as a wild card, … Read more ›...

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Blog Archives

15: Coding Scala Way – Scala concurrency & closure vs function definition

15: Q88 – Q92 Scala Functors Interview Q&As

15B: Scala Functors Interview Q&As by example

16: Coding Scala Way – Scala concurrency styles

16: Q93 – Q98 Scala monads interview Q&As

16B: Scala Monoids, Functors & Monads interview Q&As

17: Coding Scala Way – What is wrong with this code?

17: Q99 – Q103 Scala applicative functors interview Q&As

18: Q104 – Q108 Scala typeclass pattern for decoupling with polymorphism

19: Q109 – Q113 Scala ADT (Algebraic Data Types) Interview Q&As

20: Q114 – Q120 Scala fold vs reduce Q&As

21: Q121 – Q124 Scala Extractor Interview Q&As

22: What are the uses of underscore i.e _ in Scala?

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