SCALA DAY BY DAYWhat means to work with Scala. A story from a previous Java Developerby Ionut Andonescu23 April 2016, Iasi

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SUMMARY Intro (Java Evolution) Scala Refresh ( Java - to - Scala) Scala Patterns Interesting/Weird Things Questions

INTRO Java Evolution

JAVA Imperative language Statically typed Runs on JVM

JDK 1.0 (21 January 1996) …… JDK SE 8 (18 March, 2014) 

JAVA EVOLUTIONJDK SE 8 JDK SE 9

code reorganization  lightweight JSON API  JEP 286

addition of lambda expressions shift to functional programming

JEP 286: LOCAL VARIABLE TYPE INFERENCE Goal “We seek to improve the developer experience by reducing the ceremony associated with writing Java code, while maintaining Java's commitment to static type safety, by allowing developers to elide the often-unnecessary manifest declaration of local variable types.”

74%

12%

10%3%1%

What do you think of the proposed Local Variable Type In-ference feature overall? *Takipi

I think it'a great idea!

Meh, it'a OK.

I think it'a bad idea!

Not sure

Other

JEP 286: SYNTAX CHOICES var x = expr only (like C#) var, plus val for immutable locals (like Scala, Kotlin) var, plus let for immutable locals (like Swift) auto x = expr (like C++) const x = expr (already a reserved word) final x = expr (already a reserved word) let x = expr def x = expr (like Groovy) x := expr (like Go)

23.7

48.1

14

34

7.2

Possible syntax options*Takipi

var only

var and val

var and let

let only

auto only

Other

SCALA Object-functional language  Statically typed Runs on JVM First version - 20 January 2004  latest & stable version - 8 March 2016 (2.11.8)

Around 500.000 developers are using Scala * http://www.scala-lang.org/blog/2016/03/14/announcing-the-scala-center.html

SCALA REFRESH Java - to - Scala

DIFFERENCESObvious differences

semicolons variable declaration : val/var method declarations inferring type information

lazy val imported file types methods with empty argument lists options either

Syntactic Sugar and more features

partial functions ranges: 1 to n  reserved words if statement for comprehensions call by name / call by value try catch organized code in files and namespaces

JAVA CODE TO

SCALA METHODS

SCALA FUNCTIONAL

CLASS/INTERFACE CREATION

CASE CLASSES

PATTERN MATCHING

FUNCTIONS With default value

FUNCTIONS With named parameters

FUNCTIONS With nested functions

FUNCTIONS Passed as argumentReturned as value

SCALA PATTERNS Interesting/Weird Things

TUPLES

IMUTABILITY VS MUTABILITY Problem:“Separate students from a given List into separate groups: those from Romania and those outside of Romania”

IMUTABILITY VS MUTABILITY

IMUTABILITY VS MUTABILITY

IMUTABILITY VS MUTABILITY

IMUTABILITY VS MUTABILITY

MONADS

Pug monad

OPTION

EITHER

FUTURE

TRY

MAP & FLATMAPscala.util.Try

def map[U](f: T => U): Try[U]Maps the given function to the value from this Success or returns this if this is a Failure. def flatMap[U](f: T => Try[U]): Try[U]Returns the given function applied to the value from this Success or returns this if this is a Failure. ……

scala.Optiondef map[B](f: A => B): Option[B]Returns a scala.Some containing the result of applying f to this scala.Option's value if this scala.Option is nonempty. Otherwise returndef flatMap[B](f: A => Option[B]): Option[B]Returns the result of applying f to this scala.Option's value if this scala.Option is nonempty. Returns None if this scala.Option is empty. ……

WHAT MEANS TO WORK WITH SCALA?

“Unlike with many traditional functional languages, Scala allows a gradual, easy migration to a more functional style.

You can start to use it as a “Java without semicolons”. Over time, you can progress to gradually eliminate mutable state in your applications, phasing in safe functional composition patterns instead. As Scala programmers we believe that this progression is often a good idea.

At the same time, Scala is not opinionated; you can use it with any style you prefer.”

http://www.scala-lang.org/what-is-scala.html

QUESTIONS

THE END.

SCALA DAY BY DAYIonut Andonescu

23 April 2016, Iasi

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