Sample run of chapter's interpreter examples
Iterable("x", "y", "z") Map("x" -> 24, "y" -> 25, "z" -> 26) Set(Color.Red, Color.Green, Color.Blue) SortedSet("hello", "world") Buffer(x, y, z) IndexedSeq(1.0, 2.0) LinearSeq(a, b, c)
List(1, 2, 3) HashMap("x" -> 24, "y" -> 25, "z" -> 26)
List(1, 2, 3).map(_ + 1) // List(2, 3, 4): List[Int] Set(1, 2, 3).map(_ * 2) // Set(2, 4, 6): Set[Int]
def iterator: Iterator[A]
// In file collections-in-depth/iterater-example-1.scala val xs = List(1, 2, 3, 4, 5) val git = xs.grouped(3) // an Iterator[List[Int]] git.next() // List(1, 2, 3) git.next() // List(4, 5) val sit = xs.sliding(3) // an Iterator[List[Int]] sit.next() // List(1, 2, 3) sit.next() // List(2, 3, 4) sit.next() // List(3, 4, 5)
// In file collections-in-depth/set-example-1.scala val fruit = Set("apple", "orange", "peach", "banana") fruit("peach") // true fruit("potato") // false
// In file collections-in-depth/set-example-2.scala var s = Set(1, 2, 3) s += 4 s -= 2 s // Set(1, 3, 4)
// In file collections-in-depth/set-example-3.scala val s = collection.mutable.Set(1, 2, 3) s += 4 // Set(1, 2, 3, 4) s -= 2 // Set(1, 3, 4) s // Set(1, 3, 4)
def get(key): Option[Value]
// In file collections-in-depth/f.scala def f(x: String) = println("taking my time.") Thread.sleep(100) x.reverse
// In file collections-in-depth/cachedF.scala val cache = collection.mutable.Map[String, String]()
scala> def cachedF(s: String) = cache.getOrElseUpdate(s, f(s)) def cachedF(s: String): String scala> cachedF("abc") taking my time. val res16: String = cba scala> cachedF("abc") val res17: String = cba
// In file collections-in-depth/cachedF.scala def cachedF(arg: String) = cache.get(arg) match case Some(result) => result case None => val result = f(arg) cache(arg) = result result
scala> val str = 1 #:: 2 #:: 3 #:: LazyList.empty val str: scala.collection.immutable.LazyList[Int] = LazyList(<not computed>)
scala> def fibFrom(a: Int, b: Int): LazyList[Int] = | a #:: fibFrom(b, a + b) def fibFrom: (a: Int, b: Int)LazyList[Int]
scala> val fibs = fibFrom(1, 1).take(7) val fibs: scala.collection.immutable.LazyList[Int] = LazyList(<not computed>) scala> fibs.toList val res23: List[Int] = List(1, 1, 2, 3, 5, 8, 13)
val vec = scala.collection.immutable.Vector.empty val vec2 = vec :+ 1 :+ 2 // Vector(1, 2) val vec3 = 100 +: vec2 // Vector(100, 1, 2) vec3(0) // 100
val vec = Vector(1, 2, 3) vec.updated(2, 4) // Vector(1, 2, 4) vec // Vector(1, 2, 3)
collection.immutable.IndexedSeq(1, 2, 3) // Vector(1, 2, 3)
// In file collections-in-depth/immutable-queues.scala val empty = scala.collection.immutable.Queue[Int]()
// In file collections-in-depth/immutable-queues.scala val has1 = empty.enqueue(1) // Queue(1)
// In file collections-in-depth/immutable-queues.scala val has123 = has1.enqueueAll(List(2, 3)) // Queue(1, 2, 3)
scala> val (element, has23) = has123.dequeue val element: Int = 1 has23: scala.collection.immutable.Queue[Int] = Queue(2, 3)
// In file collections-in-depth/range-example-1.scala 1 to 3 // Range(1, 2, 3) 5 to 14 by 3 // Range(5, 8, 11, 14)
// In file collections-in-depth/range-example-2.scala 1 until 3 // Range(1, 2)
// In file collections-in-depth/red-black-trees-example.scala val set = collection.immutable.TreeSet.empty[Int] set + 1 + 3 + 3 // TreeSet(1, 3)
// In file collections-in-depth/bitset-example.scala val bits = scala.collection.immutable.BitSet.empty val moreBits = bits + 3 + 4 + 4 // BitSet(3, 4) moreBits(3) // true moreBits(0) // false
import scala.collection.immutable.VectorMap val vm = VectorMap.empty[Int, String] val vm1 = vm + (1 -> "one") // VectorMap(1 -> one) val vm2 = vm1 + (2 -> "two") // VectorMap(1 -> one, 2 -> two) vm2 == Map(2 -> "two", 1 -> "one") // true
// In file collections-in-depth/listmap-example.scala val map = collection.immutable.ListMap(1 -> "one", 2 -> "two") map(2) // "two"
// In file collections-in-depth/arraybuffer-example.scala val buf = collection.mutable.ArrayBuffer.empty[Int] buf += 1 // ArrayBuffer(1) buf += 10 // ArrayBuffer(1, 10) buf.toArray // Array(1, 10)
// In file collections-in-depth/listbuffer-example.scala val buf = collection.mutable.ListBuffer.empty[Int] buf += 1 // ListBuffer(1) buf += 10 // ListBuffer(1, 10) buf.toList // List(1, 10)
val buf = new StringBuilder buf += 'a' // a buf ++= "bcdef" // abcdef buf.toString // abcdef
// In file collections-in-depth/queue-example-1.scala val queue = new scala.collection.mutable.Queue[String] queue += "a" // Queue(a) queue ++= List("b", "c") // Queue(a, b, c) queue // Queue(a, b, c) queue.dequeue // a queue // Queue(b, c)
// In file collections-in-depth/queue-example-2.scala val stack = new scala.collection.mutable.Stack[Int] stack.push(1) // Stack(1) stack // Stack(1) stack.push(2) // Stack(2, 1) stack // Stack(2, 1) stack.top // 2 stack // Stack(2, 1) stack.pop // 2 stack // Stack(1)
// In file collections-in-depth/hashtable-example.scala val map = collection.mutable.HashMap.empty[Int,String] map += (1 -> "make a web site") // Map(1 -> make a web site) map += (3 -> "profit!") // Map(1 -> make a web site, 3 -> profit!) map(1) // make a web site map.contains(2) // false
// In file collections-in-depth/mutable-bitset-example.scala val bits = scala.collection.mutable.BitSet.empty bits += 1 // BitSet(1) bits += 3 // BitSet(1, 3) bits // BitSet(1, 3)
// In file collections-in-depth/array-example-1.scala val a1 = Array(1, 2, 3) val a2 = a1.map(_ * 3) // Array(3, 6, 9) val a3 = a2.filter(_ % 2 != 0) // Array(3, 9) a3.reverse // Array(9, 3)
// In file collections-in-depth/array-example-1.scala val seq: collection.Seq[Int] = a1 // ArraySeq(1, 2, 3) val a4: Array[Int] = seq.toArray // Array(1, 2, 3) a1 eq a4 // false
// In file collections-in-depth/array-example-2.scala val seq: collection.Seq[Int] = a1 // ArraySeq(1, 2, 3) seq.reverse // ArraySeq(3, 2, 1) val ops: collection.ArrayOps[Int] = a1 // Array(1, 2, 3) ops.reverse // Array(3, 2, 1)
// In file collections-in-depth/array-example-3.scala a1.reverse // Array(3, 2, 1)
// In file collections-in-depth/array-example-3.scala intArrayOps(a1).reverse // Array(3, 2, 1)
// This is wrong! def evenElems[T](xs: Vector[T]): Array[T] = val arr = new Array[T]((xs.length + 1) / 2) for i <- 0 until xs.length by 2 do arr(i / 2) = xs(i) arr
2 | val arr = new Array[T]((xs.length + 1) / 2) | ^ | No ClassTag available for T
// In file collections-in-depth/evenElems.scala // This works import scala.reflect.ClassTag def evenElems[T: ClassTag](xs: Vector[T]): Array[T] = val arr = new Array[T]((xs.length + 1) / 2) for i <- 0 until xs.length by 2 do arr(i / 2) = xs(i) arr
// In file collections-in-depth/evenElems.scala evenElems(Vector(1, 2, 3, 4, 5)) // Array(1, 3, 5) evenElems(Vector("this", "is", "a", "test", "run")) // Array(this, a, run)
scala> def wrap[U](xs: Vector[U]) = evenElems(xs) 1 |def wrap[U](xs: Vector[U]) = evenElems(xs) | ^ | No ClassTag available for U
// In file collections-in-depth/evenElems.scala def wrap[U: ClassTag](xs: Vector[U]) = evenElems(xs)
// In file collections-in-depth/string-example.scala val str = "hello" str.reverse // olleh str.map(_.toUpper) // HELLO str.drop(3) // lo str.slice(1, 4) // ell val s: Seq[Char] = str // hello
// In file collections-in-depth/equality-example.scala import collection.mutable.{HashMap, ArrayBuffer} val buf = ArrayBuffer(1, 2, 3) val map = HashMap(buf -> 3) // Map((ArrayBuffer(1, 2, 3),3)) map(buf) // 3 buf(0) += 1 map(buf) // java.util.NoSuchElementException: key not found: // ArrayBuffer(2, 2, 3)
// In file collections-in-depth/lazymap.scala def lazyMap[T, U](col: Iterable[T], f: T => U) = new Iterable[U]: def iterator = col.iterator.map(f)
// In file collections-in-depth/view-example.scala val v = Vector((1 to 10)*) // Vector(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) v.map(_ + 1).map(_ * 2) // Vector(4, 6, 8, 10, 12, 14, 16, 18, 20, 22)
// In file collections-in-depth/view-example.scala (v.view.map(_ + 1).map(_ * 2)).toVector // Vector(4, 6, 8, 10, 12, 14, 16, 18, 20, 22)
scala> val vv = v.view val vv: scala.collection.IndexedSeqView[Int] = IndexedSeqView(<not computed>)
scala> vv.map(_ + 1) val res13: scala.collection.IndexedSeqView[Int] = IndexedSeqView(<not computed>)
scala> res13.map(_ * 2) val res14: scala.collection.IndexedSeqView[Int] = IndexedSeqView(<not computed>)
scala> res14.toVector val res15: Seq[Int] = Vector(4, 6, 8, 10, 12, 14, 16, 18, 20, 22)
// In file collections-in-depth/palindrome.scala def isPalindrome(x: String) = x == x.reverse def findPalindrome(s: Iterable[String]) = s.find(isPalindrome)
// In file collections-in-depth/palindrome.scala findPalindrome(words.take(1000000))
// In file collections-in-depth/palindrome.scala findPalindrome(words.view.take(1000000))
// In file collections-in-depth/actor-example-1.scala val actors = for i <- 1 to 10 yield actor { ??? }
// In file collections-in-depth/actor-example-2.scala val actors = (1 to 10).map(i => actor { ??? })
// In file collections-in-depth/actor-example-3.scala val actors = for i <- (1 to 10).view yield actor { ??? }
// In file collections-in-depth/iterator-example-2.scala while it.hasNext do println(it.next())
// In file collections-in-depth/iterator-example-2.scala it.foreach(println)
// In file collections-in-depth/iterator-example-2.scala for elem <- it do println(elem)
// In file collections-in-depth/iterator-example-3.scala val it = Iterator("a", "number", "of", "words") val lit = it.map(_.length) it.hasNext // true lit.foreach(println) // prints 1, 6, 2, 5 it.hasNext // false
// In file collections-in-depth/iterator-example-4.scala val it = Iterator("a", "number", "of", "words") val dit = it.dropWhile(_.length < 2) dit.next() // number it.next() // of
// In file collections-in-depth/iterator-example-5.scala val (it1, it2) = it.duplicate
// This won't work def skipEmptyWordsNOT(it: Iterator[String]) = while it.next().isEmpty do {}
// In file collections-in-depth/skipEmptyWords.scala def skipEmptyWords(it: BufferedIterator[String]) = while it.head.isEmpty do it.next()
// In file collections-in-depth/iterator-buffered.scala val it = Iterator(1, 2, 3, 4) val bit = it.buffered bit.head // 1 bit.next() // 1 bit.next() // 2
// In file collections-in-depth/collection-from-scratch.scala Iterable() // An empty collection List() // The empty list List(1.0, 2.0) // A list with elements 1.0, 2.0 Vector(1.0, 2.0) // A vector with elements 1.0, 2.0 Iterator(1, 2, 3) // An iterator returning three integers. Set(dog, cat, bird) // A set of three animals HashSet(dog, cat, bird) // A hash set of the same animals Map('a' -> 7, 'b' -> 0) // A map from characters to integers
// In file collections-in-depth/list-apply.scala List.apply(1.0, 2.0)
scala> List(1, 2, 3) val res17: List[Int] = List(1, 2, 3) scala> Iterable(1, 2, 3) val res18: Iterable[Int] = List(1, 2, 3) scala> mutable.Iterable(1, 2, 3) val res19: scala.collection.mutable.Iterable[Int] = ArrayBuffer(1, 2, 3)
Iterator \Leftrightarrow java.util.Iterator Iterator \Leftrightarrow java.util.Enumeration Iterable \Leftrightarrow java.lang.Iterable Iterable \Leftrightarrow java.util.Collection mutable.Buffer \Leftrightarrow java.util.List mutable.Set \Leftrightarrow java.util.Set mutable.Map \Leftrightarrow java.util.Map
scala> import jdk.CollectionConverters.*
scala> import collection.mutable.* scala> val jul: java.util.List[Int] = ArrayBuffer(1, 2, 3).asJava val jul: java.util.List[Int] = [1, 2, 3] scala> val buf: Seq[Int] = jul.asScala val buf: scala.collection.mutable.Seq[Int] = ArrayBuffer(1, 2, 3) scala> val m: java.util.Map[String, Int] = HashMap("abc" -> 1, "hello" -> 2).asJava m: java.util.Map[String,Int] = {hello=2, abc=1}
Seq \Rightarrow java.util.List mutable.Seq \Rightarrow java.util.List Set \Rightarrow java.util.Set Map \Rightarrow java.util.Map
scala> val jul: java.util.List[Int] = List(1, 2, 3) val jul: java.util.List[Int] = [1, 2, 3] scala> jul.add(7) java.lang.UnsupportedOperationException at java.util.AbstractList.add(AbstractList.java:131)
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