Scala as Java++
Cristian Spinetta
cristian.spinetta@despegar.com
Short intro
Agenda
- Restricciones de Java
- Qué es Scala?
- Sintaxis y ejemplos
- Inmutabilidad en Scala
Tristezas Restricciones de Java
- "Evolución lenta"
- No es OO de verdad
- Verbose y MUY repetitivo
- Falta de features modernos
- Tipado a "medias"
Qué es Scala?
- Java++
- Funcional + OO
- Corre sobre la JVM
- Tipado estático + inferencia de tipos
- Conciso/expresivo
- REPL
Sintaxis: De Java a Scala
Sintaxis
Ejemplo en SCALA
Operaciones elementales
val radius: Double = 2.3;
var color: String = "red";
def area(radius: Double): Double = {
val pi: Double = 3.141592;
val sqRad: Double = radius * radius;
return pi * sqRad;
}
val description: String =
"Area is: " + area(radius);'return' implícito
val radius: Double = 2.3;
var color: String = "red";
def area(radius: Double): Double = {
val pi: Double = 3.141592;
val sqRad: Double = radius * radius;
pi * sqRad;
}
val description: String =
"Area is: " + area(radius);Ejemplo en SCALA
Operaciones elementales
Sintaxis
val radius: Double = 2.3;
var color: String = "red";
def area(radius: Double): Double = {
val pi: Double = 3.141592;
val sqRad: Double = radius * radius;
return pi * sqRad;
}
val description: String =
"Area is: " + area(radius);inferencia de tipos
val radius = 2.3;
var color = "red";
def area(radius: Double) = {
val pi = 3.141592;
val sqRad = radius * radius;
pi * sqRad;
}
val description = "Area is: " + area(radius);Ejemplo en SCALA
Operaciones elementales
Sintaxis
val radius: Double = 2.3;
var color: String = "red";
def area(radius: Double): Double = {
val pi: Double = 3.141592;
val sqRad: Double = radius * radius;
pi * sqRad;
}
val description: String =
"Area is: " + area(radius);val radius = 2.3;
var color = "red";
def area(radius: Double) = {
val pi = 3.141592;
val sqRad = radius * radius;
pi * sqRad;
}
val description = "Area is: " + area(radius);; opcional
val radius = 2.3
var color = "red"
def area(radius: Double) = {
val pi = 3.141592
val sqRad = radius * radius
pi * sqRad
}
val description = "Area is: " + area(radius)Ejemplo en SCALA
Operaciones elementales
Sintaxis
val radius = 2.3
var color = "red"
def area(radius: Double) = {
val pi = 3.141592
val sqRad = radius * radius
pi * sqRad
}
val description = "Area is: " + area(radius){ } opcional
val radius = 2.3
var color = "red"
def area(radius: Double) = 3.141592 * radius * radius
val description = "Area is: " + area(radius)Ejemplo en SCALA
Operaciones elementales
Sintaxis
val radius = 2.3
var color = "red"
def area(radius: Double) = 3.141592 * radius * radius
val description = "Area is: " + area(radius)String interpolation
val radius = 2.3
var color = "red"
def area(radius: Double) = 3.141592 * radius * radius
val description = s"Area is: ${area(radius)}"Ejemplo en SCALA
Operaciones elementales
Sintaxis
public class User {
private Integer id;
private String name;
private LocalDate birthday;
public User(Integer id, String name,
LocalDate birthday) {
this.id = id;
this.name = name;
this.birthday = birthday;
}
public Integer getId() { return id; }
public void setId(Integer id){ this.id = id;}
// Getter and Setter for rest of fields...
@Override
public boolean equals(Object o) {
// usually a lot of code...
}
@Override
public int hashCode() {
// more code!
}
}case class User(id: Int,
name: String,
birthday: LocalDate)JAVA
SCALA
DTO
- Constructor
- Getters (y Setters si hay var)
- copy()
- toString()
- equals() y hashCode()
Sintaxis
def sort(xs: Array[Int]) {
def swap(i: Int, j: Int){
val t = xs(i); xs(i) = xs(j); xs(j) = t
}
def sort1(l: Int, r: Int) {
val pivot = xs((l + r) / 2)
var i = l; var j = r
while(i <= j) {
while(xs(i) < pivot) i += 1
while(xs(j) > pivot) j -= 1
if (i <= j) {
swap(i, j)
i += 1
j -= 1
}
}
if(l < j) sort1(l, j)
if(j < r) sort1(i, r)}
sort1(0, xs.length - 1)
}def sort(xs: Array[Int]): Array[Int] = {
if (xs.length <= 1) xs
else {
val pivot = xs(xs.length / 2)
Array.concat(
sort(xs filter (pivot >)),
xs filter (pivot ==),
sort(xs filter (pivot <)))
}
}Imperativo
Funcional
Versátil y expresivo
Sintaxis
Ejemplo: Quick Sort
Todas las operaciones están implementadas en la librería standard de Scala.
No hay soporte especial del compilador.
Scala permite programar de forma imperativa/objetosa o bien con un estilo funcional.
Inmutabilidad
en Scala
Los valores asignados no cambian
Inmutabilidad
A balanced attitude for Scala programmers
“Prefer vals, immutable objects, and methods without side effects. Reach for them first. Use vars, mutable objects, and methods with side effects when you have a specific need and justification for them.”
scala> val name = "Peter"
name: String = Peter
scala> name = "Paul"
<console>:8: error: reassignment to val
name = "Paul"
^Variable inmutable
scala> val names = List("Peter", "Paul")
names: List[String] = List(Peter, Paul)
scala> names :+ "Moley"
res0: List[String] = List(Peter, Paul, Moley)Lista inmutable
Ejemplo: Cuenta bancaria
Inmutabilidad
class BankAccount {
var balance = 0
def deposit(amount: Int) {
if (amount > 0) balance += amount
else balance
}
def withdraw(amount: Int): Int =
if (amount >= 0 && amount <= balance) {
balance -= amount
balance
} else {
println("insufficient funds")
balance
}
}
Con mutabilidad
val account = new BankAccount
account.deposit(30) // return 30
account.deposit(20) // return 20
account.withdraw(10) // return 10
// Current balance: 40case class BankAccount(balance: Int) {
def deposit(amount: Int) =
if (amount > 0)
BankAccount(balance = balance + amount)
else
this
def withdraw(amount: Int) =
if (amount >= 0 && amount <= balance) {
BankAccount(balance = balance - amount)
} else {
println("insufficient funds")
this
}
}Con inmutabilidad
BankAccount(0)
.deposit(30) // return a new BankAccount
.deposit(20) // return a new one
.withdraw(10) // return a new one
// Balance in the last BankAccount: 40Inmutabilidad: No se cambia el valor, se crea uno nuevo.
Instalar Scala + SBT + Intellij IDEA: