xx1. おまけ

Scala の メソッド は、

・引数が０個の場合は、メソッド名の後ろの ( ) を省略できる。

・オブジェクト と メソッド と 引数 を 演算子 の様に中間記法で表記できる。

・演算子 を メソッド呼び出しの表記法で利用できる。（実は演算子は ただのメソッド）

・メソッドの部分適用から関数オブジェクトを得ることが出来る。

scala> def a() = 123

a: ()Int

scala> a()

res0: Int = 123

scala> a

res1: Int = 123

scala> object o { def a()=234; def b(x:Int) = x}

defined object o

scala> o.a

res2: Int = 234

scala> o.b(345)

res3: Int = 345

scala> o b 345

res4: Int = 345

scala> o.b(_:Int)

res6: Int => Int = <function1>

scala> o.b(_:Int)(456)

<console>:9: error: Int does not take parameters

o.b(_:Int)(456)

^

scala> (o.b(_:Int))(456)

res8: Int = 456

scala> object oo { def c(x:Int,y:Int) = x-y}

defined object oo

scala> oo.c(_:Int,_:Int)

res9: (Int, Int) => Int = <function2>

scala> oo.c(_:Int,_:Int).curried

<console>:9: error: value curried is not a member of Int

oo.c(_:Int,_:Int).curried

^

scala> (oo.c(_:Int,_:Int)).curried

res11: Int => (Int => Int) = <function1>

scala> (oo.c(_:Int,_:Int)).curried 1 2

<console>:1: error: ';' expected but integer literal found.

(oo.c(_:Int,_:Int)).curried 1 2

^

scala> (oo.c(_:Int,_:Int)).curried (1) (2)

res12: Int = -1

scala> object ooo { def c(x:Int)(y:Int) = x-y}

defined object ooo

scala> ooo.c (1)

<console>:9: error: missing arguments for method c in object ooo;

follow this method with `_' if you want to treat it as a partially applied function

ooo.c (1)

^

scala> ooo.c (1) (2)

res15: Int = -1

scala> (ooo.c (1)) (2)

res16: Int = -1

scala> ooo.c(1) (_:Int)

res17: Int => Int = <function1>

scala> val aaa = ooo.c(1) (_:Int)

aaa: Int => Int = <function1>

scala> aaa (1)

res18: Int = 0

Stream

// 0 1 2 3 の遅延ストリーム

Stream.from(0)

val ls = List(1,2,3)

val ss = Stream(4,5,6)

scala> ls ::: ls

List[Int] = List(1, 2, 3, 1, 2, 3)

scala> ls.toStream #::: ss

res5: scala.collection.immutable.Stream[Int] = Stream(1, ?)

関数の引数の名前渡しで遅延評価

def f( a:Int , b: => Int)