[Start] Scala

Do you know
Object-oriented
Programming?

Do you know
Functional
Programming?

Do you know
Scala?
’’’

[Start]
Scala!
’’’

@mumoshu

# of atnders
php
java
scala
js
python
perl
0 5 10 15

PHP, Java, Scala
Web dev General Purpose

Scala

PHP Java

PHP, Java, Scala

Dynamically Statically typed
typed Scala

PHP Java

PHP, Java, Scala
Shorter code
Dynamically Statically typed
typed Scala

Longer code
PHP Java

Scala

• has NOTHING NEW!

PHP and Scala

• PHP + Static Typing + Shorter code
= Scala ?!

Java and Scala

• Java + Shorter code
= Scala ?!

Basic computation
• Calculate the sum in imperative style

Basic computation

1 + 2 + 3 = 6

Basic computation

1 + 2 + 3 = 6

sum = 0
sum = sum + 1
sum = sum + 2
sum = sum + 3

MY Ranking

1. (Ruby)
2. Scala
3. (JavaScript)
4. PHP
5. Java

Sum with Java

int[] array = new int[] { 1, 2, 3 };
int sum = 0;
for (int i=0; i<array.length; i++) {
sum += array[i];
}
System.out.println(sum);

Sum with PHP

$array = array(1, 2, 3);
$sum = 0;
for ($i=1; $i<=count($array); $i++) {
$sum += $array[$i];
}
print $sum;

Sum with PHP

$sum = 0;
for ($i=1; $i<=count($array); $i++) {
$sum += $array[$i];
}
print($sum);

Sum with JS

var array = [1,2,3]
var sum = 0
for (var i in array) {
sum += array[i]
}
console.log(sum);

Sum with Ruby
array = [1, 2, 3]
sum = 0
for (x in array)
sum += x
end
puts sum

Scala + for

var array = Array(1, 2, 3)
var sum = 0
for (x <- array) {
sum += x
}
println(sum)

(‘-’) Is that your
power?

Scala + foreach
var sum = 0
array foreach { x =>
sum += x
}
println(sum)

Scala + foreach
var sum = 0
array foreach {
sum += _
}
println(sum)

Sum with `reduce`
• Calculate the sum in functional styl

Sum with `reduce`
• Calculate the sum in functional style

sum = 1 + 2 + 3
sum = 3 + 3
sum = 6

Sum with `reduce`

sum = 1 + 2 + 3

Sum with `reduce`
1. (Ruby)
2. Scala
3. (JavaScript)
4. PHP
5. Java

PHP

function reduce($a, $b){
return $a + $b;
};
$sum = array_reduce($array, 'reduce');
print $sum;

JavaScript

var array = [1, 2, 3];
var sum = array.reduce(function(a,b){
return a + b
});
console.log(sum);

Ruby

array = [1, 2, 3]
sum = array.reduce(&:+)
puts sum

Scala

val array = Array(1, 2, 3)
val sum = array.reduce(_+_)
println(sum)

More Scala

val array = Array(1, 2, 3)
val sum = array.sum
println(sum)

You learn everyday

• And you code gets BETTER

Are you

• a Java engineer?
• or maybe a PHP engineer?
• Do you use `Class’?

Class
• Define a class in
1. Scala
2. (Ruby)
3. PHP
4. Java
5. (JavaScript)

Greeter
Hello Scala

Greeter

Classes in Java
public class Greeter {
private String name;

public Greeter(String name) {
this.name = name;
}

public Greeter() {
Greeter(“Scala”);
}

public String getName() {
return this.name;
}

public void greet() {
System.out.println(“Hello “ + this.name);
}
}

Greeter greeter = new Greeter("Scala!");
greeter.greet();

Classes in PHP
<?php
class Greeter {
private $name;

function __construct($name = 'Scala') {
$this->name = $name;
}

public function getName() {
return $this->name;
}

public function greet() {
print ‘Hello ‘ . $this->name;
}
}

$greeter = new Greeter(‘Scala!’);
$greeter->greet();
?>

Classes in JS
function Greeter(name) {
this.name = typeof name == “undefined” ? “Scala” : name;
}

Greeter.prototype = {
getName: function() {
return this.name;
},
greet: function() {
console.log(“Hello “ + this.name);
}
};

var greeter = new Greeter(“Scala”);
greeter.greet();

Classes in Ruby
class Greeter
attr_reader :name
def initialize(name="Scala")
@name = name
end
def greet
puts “Hello “ + @name
end
end

greeter = Greeter.new(“Scala”)
greeter.greet

Classes in Scala
class Greeter(val name: String = “Scala”) {
def greet() {
println(“Hello “ + name)
}
}

val greeter = new Greeter("Scala!");
greeter.greet()

break
1/2

ビースト★ハーレム
∼野獣の甘噛み∼

http://pf.gree.jp/56616

Scala is

• General purpose
• Not only Web
• Multi-paradigm
• Object-oriented + Functional
programming

Scala

’’’
• Run on JVM
• A lot of Java libraries
• Hybrid language
• Imperative programming
• Object oriented programming
• Functional programming

Whats happy with FP

• Concurrency
• Scalability

Imperative vs
Functional
• Imperative Programming

do A -> state++,
do B -> state++, ...


in1 -> f(x) -> out1
in2 -> g(x) -> out2

Easy concurrency
• Imperative programming

do A -> state <- do B
> sudden conflict!!! <


in1 -> f(x) -> out1, in2 -> g(x) -> out2
> no conflict!!! <

Dynamic vs Static
typing

• About type-safety

Dynamic typing

• GOOD
• Run anyway
• BAD
• More runtime errors

Call to undefined
function

Static typing

• GOOD
• More compile errors
• BAD
• Hard to read error messages

Scala 2.10

• We have Scala 2.9.3
• Scala 2.10 is coming (on 12/26?)

Recommendation

• If you want to:
• write something other than Web app
• write noise-free, consise code
• develop your skill GRADUALLY

Scala for business

• Scalaはお仕事に向いてます

• Java同様、静的型付けは複数人での
開発に有効

• Scalaはエンジニアの成長を止めない

Scala for education
• ステップアップ学習に最適

• sumの例のように、Scalaに慣れてくる
と徐々に簡潔な書き方が出来るよう
になっていく

• 手続き的に書ける。慣れたらいつで
も関数型チックに書ける。

Scala’s flexibility
• Scalaは自由度が高い

• 同じ意味のことを幾通りにも書けて
メンテナンス性が悪い、のではない

• 各人のレベルにあった記述ができる

• プログラマの創造性を阻害しない

Learning Scala

• Javaと同じ書き方でいいなら、Javaと同じ学
習コスト

• ちょっと短いだけのJavaとして書けるので

• Web開発ならPHPの方が最初の敷居が低い

REPL
• Scalaの対話環境

• ScalaのREPLを起動すると”Welcome to
Scala”って言われる

• 「ようこそScalaへ。ご命令を。」って
言ってくれるScalaかわいい

Compilation time

• Scalaのコンパイルは長い

• Time is money
• PCをスペックアップしましょう

[Start] Scala

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