Skip to main content

Scala

Why Scala?

  • Criado em 2004
  • Integra com java
  • Integração gradual com funcionalidades funcionais

Variables​

val is an immutable variable var is a mutable variable

Types​

  • Scala has type inference
  • Deve-se evitar type tests e casts
  • Built-ins
    • Byte: 8 bit int (-128 to 127)
    • Short: 16 bit integer (-32768 to 32767)
    • Int: 32 bit int - 2 billion to + 2 billion
    • Long: 64 bit integer (-2^63 to 2^63-1)
    • Float: 32 bit single precision float
    • Double: 64 bit single precision float
    • Boolean: true or false
    • Char: unicode char
    • String: sequence of chars
    • BigInt
    • BigDecimal

Immutable Collections​

  • Seq: have defined order Seq(1, 1, 2)
  • Set: no duplicates Set(1, 1, 2)
  • List: standard linked list List(1, 1, 2)
  • Array
  • Map: key value containers Map('a' -> 1, 'b' -> 2)

Mutable Collections​

  • HashMap:
  • ListBuffer
  • ArrayBuffer
  • LinkedList
  • PriorityQueue
  • Stack
  • StringBuilder

Map​


val ratings = Map(
    "Lady in the Water"  -> 3.0,
    "Snakes on a Plane"  -> 4.0,
    "You, Me and Dupree" -> 3.5
)

Yield​

The yield keyword means that I want to yield a new collection from the existing collection that I’m iterating over in the for-expression, using the algorithm shown.”

String manipulations​

val name = s"$firstName $mi $lastName"
// or

val name = s"Name ${firstName} ${mi} ${lastName} has ${2 + 2} years"

""" Inline
sucks so use
multiple """

println adds a line after string while print only adds a word

Control Structures​

  • For
  • While
  • try catch finally
  • If then else
  • Match expressions
    • são bastante importantes

Classes​

classes on scala don't allow static methods

There is a special type of classes called case classes

Traits​

Are like interfaces in Java

Objects​

Are like classes but for every definition has one single instance.

Packages​

Formatação​

  • Default é 2 espaços de identação

Naming convention​

  • Class Names - StoreEmployee
  • Variable - firstName
  • Methods - toUpper

Tips​

  • Evita usar o return
  • Evita variáveis mutáveis

Principios para tornar um código funcional​

  • reduce side-effects (no mutating state)
  • Referential transparent
    • Idempotent is referential transparent but may not be the other way around (ƒ(x) ≠ ƒ(ƒ(x))) !=
  • Be immutable

Pure function advantages

  • Reduces race conditions
  • less complex
  • readability

Function that can accept and/or return a function

Linked lists are the bread and butter of functional programming

Functional composing​


// Compose creates a function that composes other functions
val fComposeG = f _ compose g _  //== f(g())

fComposeG("Yay")

// andThen composes but calls the functins by order

f _ andThen g _ # g(f())

Partial functions​

Polymorphism​

Has rank-1 polymorphism

Persistent data structures and structural sharing​

Creates versions for each update and shares common data between versions

Partial and full structural sharing: use part of the full data structure between versions

Strict vs Lazy (non strict)

Strict is where all arguments of a function are evaluated before executing

Chaining → Linked List

Hash Table

  • Modifications require whole copy of table
  • Scala uses Tries to optimize hash tables

Hash Tries

  • Each node has a number of children (Base N)
  • Each entry has a hash number that facilitates search

Use optional params not overloading

  • Case class automattically adds functions like comparison, applies, etc

Pattern matching​

Extractors

  • Extracts properties contained in the case

Folding​

Folding vs Reduce

  • Folding requires an initial value

Category​

  • Category properties
    • Identity
    • Composition

Functor : Mapping of objects from a category into another

  • Nil is for Lists and None is for Options

Programming Languages

Specs​

Scala School specs

We can nest behaviour inside each Spec

  • doBefore & doAfter
  • doFirst & doLast

Resources​

learnxinyminutes Scala School