Learning Scalaの第1章〜第5章まで

Learning Scalaの第1章〜第5章までの例文を順番にまとめました。
Scalaをこれから始める人向けに、難しいところに入る前に構文の書き方的な部分から見ていただければと思います。

Transcript

1. LearningScalaͷୈ1 ষʙୈ5ষ͙Β͍ 2016/07/10 ୈ3ճScalaؔ੢ษڧձ
2. About ME • ԬాཾҰ (@ryu1_okd) • גࣜձࣾάϥουΩϡʔϒ • SiTest • Node.js / LiveScript / AngularJS • Docker / CoreOS / fleet / etcd
3. ຊ೔ͷൃදʹ͍ͭͯ Scala͜Ε͔ΒؤுΔΑͬͯਓ (ൃදऀ΋ಉ͡)
4. Learning Scala Practical functional programming for tha JVM • ग़൛ࣾɿO'Reilly • ൃച݄ɿ2014/12
5. Learning Scala • Part1. CoreScala • 1: Getting Started with the Scala Language. • 2: Working with Data: Literals, Values, Variables, and Types. • 3: Expressions and Conditionals. • 4: Functions • 5: First-Class Functions.
6. Scala ScalaʢεΧʔϥʔ([ˈskɑːlɑː] skah-lah[1])[2]ʣ͸ΦϒδΣΫτࢦ ޲ݴޠͱؔ਺ܕݴޠͷಛ௃Λ౷߹ͨ͠ϚϧνύϥμΠϜͷϓϩά ϥϛϯάݴޠͰ͋Δɻ໊લͷʮScalaʯ͸ӳޠͷʮscalable languageʯʹ༝དྷ͢Δ΋ͷͰ͋Δɻ wikipedia:Scala
7. Install Scala • http://www.scala-lang.org/
8. Literals val <name>: <type> = <literal> val x: Int = 5 val x = 5
9. Values / Variables scala> val x = 5 x: Int = 5 scala> x = 10 <console>:11: error: reassignment to val x = 10 ^
10. Values / Variables scala> var y = 5 y: Int = 5 scala> y = 10 y: Int = 10 scala> y = "Hello" <console>:11: error: type mismatch; found : String("Hello") required: Int y = "Hello" ^
11. An Overview of Scala Types
12. Expression scala> val x = 5 * 20; val amount = x + 10 x = 100 amount = 110 Block͸{}ͰғΉ scala> val amount = { | val x = 5 * 20 | x + 10 | } amount: Int = 110
13. If/else ࡾ߲ԋࢉࢠ͸ͳ͍ scala> if ( 10 > 0) println("hoge") else println("fuga") hoge
14. match/case otherwise ຢ͸ _ Λ࢖͏ scala> val status = 500 scala> val message = status match{ | case 200 => "ok" | case 400 => println("ERROR 400"); "error" | case _ => { | println("ERROR 500") | "error" | } | } ERROR 500 message: String = error
15. Matching Types with Pattern Variables ܕͰͷmatch/case scala> val x:Int = 12180 x: Int = 12180 scala> val y:Any = x y: Any = 12180 scala> y match { | case x: String => s"'x'" | case x: Double => f"$x%.2f" | case x: Float => s"$x%.2f" | case x: Long => s"${x}l" | case x: Int => s"${x}i" | } res0: String = 12180i
16. Loops scala> for (x <- 0 to 3) { println(s"loop $x")} loop 0 loop 1 loop 2 loop 3 scala> for (x <- 0 to 3) yield { s"loop $x"} res1: scala.collection.immutable.IndexedSeq[String] = Vector(loop 0, loop 1, loop 2, loop 3) scala> for (x <- 1 to 10 if x % 3 == 0) println(x) 3 6 9
17. Nested Iterators scala> for { | x <- 1 to 2 | y <- 1 to 3 | } | { println (s"($x, $y)") } (1, 1) (1, 2) (1, 3) (2, 1) (2, 2) (2, 3)
18. Functions def <identifier> = <expression> def hi: String = "hi" def hi = "hi" scala> def multiplier(x:Int, y:Int): Int = { | x * y | } multiplier: (x: Int, y: Int)Int scala> multiplier(6, 7) res3: Int = 42
19. Procedures scala> def log(d: Double): Unit = println(f"Got value $d%.2f") log: (d: Double)Unit scala> log(2.235353) Got value 2.24
20. Calling Functions with Named Parameters scala> def greet(prefix: String, name: String) = s"$prefix $name" greet: (prefix: String, name: String)String scala> val greeting1 = greet("Ms", "Brown") greeting1: String = Ms Brown scala> val greeting2 = greet(name = "Brown", prefix = "Mr") greeting2: String = Mr Brown
21. Parameters with Default Values scala> def greet(prefix: String = " ", name: String) = s"$prefix$name" greet: (prefix: String, name: String)String scala> val greeting1 = greet(name = "Paul") greeting1: String = " Paul" scala> val greeting2 = greet("Paul") <console>:11: error: not enough arguments for method greet: (prefix: String, name: String)String. Unspecified value parameter name. val greeting2 = greet("Paul") ^
22. Type Parameters identityʹStringΛ౉͢ͱStringͰฦ͢ identityʹIntΛ౉͢ͱIntͰฦ͢ scala> def identity(a: Any): Any = a identity: (a: Any)Any scala> val s:String = identity("Hello") <console>:11: error: type mismatch; found : Any required: String val s:String = identity("Hello") ^
23. Type Parameters scala> def identity[A](a: A): A = a identity: [A](a: A)A scala> val s: String = identity[String]("Hello") s: String = Hello scala> val i: Int = identity[Int](123) i: Int = 123 scala> val d: Double = identity(3.1415) d: Double = 3.1415 scala> val f = identity(3.1415f) f: Float = 3.1415
24. Function Types and Values ([<type>, ...]) => <type> scala> def double(x: Int): Int = x * 2 double: (x: Int)Int scala> double(5) res3: Int = 10 scala> val myDouble: (Int) => Int = double myDouble: Int => Int = <function1> scala> myDouble(10) res4: Int = 20
25. Higher-Order Functions ߴ֊ؔ਺ɹؔ਺ΛҾ਺ʹ࣋ͭؔ਺΍ؔ਺Λฦؔ͢਺ scala> def safeStringOp(s: String, f: String => String) = { | if(s != null) f(s) else s | } safeStringOp: (s: String, f: String => String)String scala> def reverser(s: String) = s.reverse reverser: (s: String)String scala> safeStringOp(null, reverser) res5: String = null scala> safeStringOp("ABCDEFG", reverser) res6: String = GFEDCBA
26. Partially Applied Function and Currying ෦෼ద༻ scala> def factorOf(x: Int, y: Int) = y % x == 0 factorOf: (x: Int, y: Int)Boolean scala> val multipleOf3 = factorOf(3, _: Int) multipleOf3: Int => Boolean = <function1> scala> val y = multipleOf3(78) y: Boolean = true
27. Partially Applied Function and Currying ΧϦʔԽ scala> def factorOf(x: Int)(y: Int) = y % x == 0 factorOf: (x: Int)(y: Int)Boolean scala> val isEven = factorOf(2) _ isEven: Int => Boolean = <function1> scala> val z = isEven(32) z: Boolean = true
28. Invoking Higher-Order Functions with Function Literal Blocks scala> def safeStringOp(s: String, f: String => String) = { | if (s != null) f(s) else s | } safeStringOp: (s: String, f: String => String)String scala> val uuid = java.util.UUID.randomUUID.toString uuid: String = 6c70d5ca-c7ce-4675-8671-e27ebd88d58d scala> val timedUUID = safeStringOp(uuid, { s => | val now = System.currentTimeMillis | val timed = s.take(24) + now | timed.toUpperCase | }) timedUUID: String = 6C70D5CA-C7CE-4675-8671-1468053661358
29. ·ͱΊ • ίοϓຊΑΓಡΈ΍͍͢ • ༸ॻ͔ͩΒͱܟԕ͠ͳͯ͘΋ྑ͍ • લ൒͸֤߲ͷλΠτϧͱίʔυྫͰͳΜͱͳ͘ཧղͰ͖Δ • ScalaΛମܥతʹֶΜͰ͖ͨΘ͚Ͱ͸ͳ͍ͷͰͪΐ͏Ͳ͍͍ৼ ΓฦΓʹͳͬͨ • ஌Βͣʹ࢖͍ͬͯͨ͜ͱ΍৽͍͠ൃݟ΋͋Δ
30. ͝ਗ਼ௌ͋Γ͕ͱ͏͍͟͝·ͨ͠ɻ