Programming in Scala (Second Edition) reading notes 4

The 1.Tuple and list are immutable objects (Immutalbe), but the elements of a tuple can be of different types

Val mytuple = ("A", 1, "Park", 3.13359) println (mytuple._1)//A println (mytuple._2)//1 println (Mytuple._3) Park

Creating a tuple simply put the element in parentheses and create an instance of the Tuple4 class, as defined by Tuple4 in Scala.

/** a tuple of 4 elements; the canonical representation of a  [[scala. product4]]. * *   @constructor   Create a new tuple with  4 elements. note that it is more idiomatic to create a  tuple4 via  ' (t1, t2, t3, t4)  *   @param   _1    Element 1 of this Tuple4 *   @param   _2    element 2 of this tuple4 *   @param   _3   element  3 of this Tuple4 *   @param   _4   element 4  of this tuple4 */@deprecatedInheritance ("tuples will be made final  in a future version. ", " 2.11.0 ") Case class tuple4[+t1, +t2, +t3,  +T4] (_1: T1, _2: T2, _3: T3, _4: T4)   extends Product4[T1,  T2, t3, t4]{  override def tostring ()  =  "("  + _1 +   ","  + _2 +  ","  + _3 +  ","  + _4 +  ")"    }

A tuple like 5 elements is an instance of Tuple5, and a tuple of 6 elements is an instance of Tuple6

So you can explain why you use _1, _2, _3, and so on to refer to elements in a tuple.

The type parameter in the TUPLE4 definition is preceded by a + sign, which represents the Covarience parameter and will be explained in depth later

2. Set has two types, immutable and mutable, with the same name, creating immutable set objects by default

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var jetSet = Set ("Bench", "Audi", "Tesilla") JetSet + = "Luhu" println (Jetset.contains ("Bicycle"))

To add a new element to a set, you call + on the set, passing in the new element. Both mutable and immutable sets offer A + method, but their behavior

Differs. Whereas a mutable set would add the element to itself, an immutable

Set would create and return a new set with the element added

For immutable set, the + operation creates a new set

For Mmutalbe set, the + operation adds an element to its own

3. Map is similar to set and there are two implementations of Immuatlbe and mutable

4. Reading files

Import Scala.io.Sourceobject Testmain {def main (args:array[string]) {var lines = Source.fromfile ("E:/testread.txt"). G Etlines Lines.foreach (println)}}

Programming in Scala (Second Edition) reading notes 4