From Ruby to Scala

TEST

HELLO

Hello, is there Rubyist?

From Ruby to

Scala

@todeskinghttps://www.flickr.com/photos/7armyjmtc/14249465709

(When I moved)

Who:

@todeskinguses twitter and GitHub

web: todesking.com

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Working at

My background

• Sistem Integrator(2008-2012)• Buisiness batches• Recommendation system• With Java

• Social game servicer• Browser based social game server• With Rails

• DSP servicer• Adverting technology(Real-time bidding, user trakcing,

machine learning)• With Scala

• Vim

What is DSP

• "Demand Side Platform"• You can find detailed description in at

Internet.

Ad Client

sDSP SSP

real time bidding(RTB)

Web PagesI'm here

Today I NOT talk to:

• How to build high-performance system• DO THE RIGHT THING and KEEP GOING,

thats all.• How to speed up compilation time

• BUY FASTER MACHINE• Whitch is greatest language

• Every language has own good things• 😃😃😃BE PEACEFUL😃😃😃

I moved from Rubyto Scala, in this April

• That is smoother than I thought.• Basically, Ruby and Scala has common

attributes• object-oriented and functional paradigm• Modern features for productivity and fun

Ruby and Scala is Class-based Object Oriented language

• Class based object oriented language

class Person < Struct.new(:name, :age) def hello puts "Hello there, my name is #{name}." endend

class Person(val name:String, val age:Option[Int]) { def hello():Unit = { println(s"Hello there, my name is ${name}.") }}

At first: Common attributes of Ruby and Scala

• Class based object oriented language with functional features

def sumOfAge(people:Seq[Person]):Int = { people.map(_.age).flatten.foldLeft(0)(_ + _)}

def sum_of_age(people) people.map(&:age).compact.reduce(0, &:+)end

At first: Common attributes of Ruby and Scala

• "Fun" language• "Ruby をキメると気持ちいい "(Matz)

• I can't translate it...• 　 → 💉 😋😊😆

• "Maybe most important is that programming in Scala tends to be very enjoyable."

Today's theme:How these languages do things in different way

Class definition

class Person < Struct.new(:name, :age)end

person = Person.new("tode sking", 31)

class Person(val name:String, val age:Option[Int])val person = new Person("tode sking", Some(31))

Class definition in Ruby

class Person < Struct.new(:name, :age)

WHAT?!Creating new instance at class definition?!?!

"class" for class definition

"<" means "extends"

Create new instance of Struct

Let's begin most plain case

class Person def initialize(name, age) @name = name @age = age end def name; @name; end def name=(val); @name = val; end def age; @age; end def age=(val); @age = val; endend

"def" for method definition

method named "initialize" is treated as

ctor

"@name" is instance variable

getter and setter methods

Lot of boilerplate😩

Auto generating accessor method in Ruby

class Person def initialize(name, age) ... attr_reader :name attr_reader :ageend

"attr_reader" is keyword for generating accessor method

"attr_writer" and "attr_reader" is also

available

NO, actually it is not KEYWORD

It just a METHOD.

Auto generating accessor method in Ruby

attr_accessor :name

≒define_method("name") { @name }define_method("name=") {|val| @name = val }

def name; @name; enddef mane=(val); @name = val; end

≒

Ruby is DYNAMIC language

• EVERYTHING is object• Class is object too• o = Object.new; o.class => Object• If you want to create new class, try A =

Class.new• (assign constant A to fresh class object)

• To define a method to A, try A.define_method(:foo){...}• (actually, define_method is "private". You

should use A.instance_eval { define_method(:foo) ... })

It called "Macro" in Ruby

• Such method called "macro"(Actually, it is just a method!!)

• Ruby has no "compile-time". all execution is in "runtime"

Defining accessor method: Ruby and Scala

• scala• var foo• roughly equal to { private[this] var foo_;

def foo = foo_ }• specialized syntax for accessor

• Ruby• attr_*• Enhance class definition with DSLs

Auto generating accessor method in Ruby

class Person < Struct.new(:name, :age)

Create a new instance of Struct

Struct is a kind of Class

PersonBase = Struct.new(:name, :age)class Person < PersonBase

≒

Auto generating accessor method in Ruby

Struct.new(:name, age) returns class that like

class (unnamed) def initialize(name, age) @name, @age = name, age end attr_accessor :name attr_accessor :age # other utility methods...end[

Class definition

class Person < Struct.new(:name, :age)end

person = Person.new("tode sking", 31)

class Person(val name:String, val age:Option[Int])val person = new Person("tode sking", Some(31))

Function as value

• Scala:• val f:Int => Int = _ + 1• f(1) //=> 2• val g:Any => String = _.toString

• Ruby• f = ->(x){x + 1}• f.call(1) or f[1] or f.(1)• mehod and value is strongly separated• g = ->(x){x.to_s}

Functions as value in other languages

• Scheme: f, (f a b)• javascript: f, f(a, b)• Common Lisp: #'f, (f a b), (funcall #'f (list

arg1 arg2))

Use function as value: Scala case

• def foo(x:Int):String• val f = foo // not works• val f = foo _ // works• def bar(f:Int => String)• bar(foo) // works• bar(x => x.toString)• bar { x => x.toString }• bar(_.toString)

Use function as value: Ruby case

• def foo(x)• f = method(:foo)• f = ->(x){ foo(x) }• def bar1(f)• def bar2(&f)• bar1(f)• bar2 {|x| foo(x) }• bar2(&f)

Use any object as function

• [1, 2, 3].map(&:to_s) #=> ["1", "2", "3"]• map(&:to_s) • It behave like Scala's map(_.toString)• If block value is given, Ruby runtime call its

"to_proc" method and use the result value as block.

• Ruby's Symbol class has to_proc method• :to_s.to_proc #=> {|obj| obj.to_s }

Collections

• Literals• Ruby: {}, []• Scala: ()

• Neither list nor hash literals

Collections

TupleN

Map HashMapLinkedHashM

apHashMap

Seq

immutable

LinkedHashMap

List

Stack

mutable

Buffer

Traversable

Array

Hash

Enumerable

{key => value}

[1, 2, 3]

(a, b)

Ruby has "Big" classes

• "Array" is generic, mutable data structure, it can, push/pop, shift/pop, insert, indexed and sequential access, and also used as tuple

• "Hash" is generic, mutable (and only) key-vakue map structure in Ruby standard library

Transform collection in Big-class style

• [1, 2, 3].map(&:to_s) #=> ["1", "2", "3"]• Ruby has few Big collection classes.

Everything goes simple.

Transform collection in Scala

• Iterator[A].map(f:A => B):Iterator[B]• List[A].map(f:A => B):List[B]• BitSet.map(f:Int => Int):BitSet• BitSet.map(f:Int =>

String):SortedSet[String]• Magic "CanBuildFrom" implicit argument is

used to solve this problem.• def map[B, That](f: (Int) ⇒ B)(implicit bf:

CanBuildFrom[A, B, That]): That• Scala used types VERY MUCH.It's cool.

How to ehnahce existing class in Scala

• implicit conversion• subclassing

How to ehnahce existing class in Ruby

• subclassing• direct modification(simplly

overwrite/alias_method_chain)• define singleton method• include/extend• refinements

How to handle "non-existens value"

• Scala: Option[T]• Ruby: ♥nil♥

• false and nil is "falsy". Other values are "truthy".

• obj.foo if obj # call obj.foo if obj is not nil• obj.try(:foo) # same (ActiveSupport

feature)

Conclusion

• Ruby and Scala is very different, but they share same goal: be productive, be fun.

• There are many different approach to solve problems.We can learn things and achieve fresh surprise from other culture.

Have a fun with various programming!!

Today I want talk to:• Libraries

• rubygems: High accessibility• Source distribution• Easy to publish

• maven repo: Top on Java ecosystem• Some impedance missmatch• Binary distribution• Bit difficult to publish, especially official repo.

• Build/Task system• Rake: Simple scripting with internal DSL• Sbt: Type-safe and immutable dependency graph construction with cool := ++=

<<= s• It's Scala's way!!

• Community• Ruby: Humanity

• Love emotional context• Scala: Types

• Love Monads !!!!