Hello, Habr. For future students of the "Scala-developer" course, we prepared a translation of the material.
We also invite you to the open webinar "Effects in Scala" . Participants, together with an expert, will consider the concept of effect and the complexity that may arise if they exist, as well as consider the concept of a functional effect and its properties.
What is Scala 3?
Scala 3 is the new major version of the Scala programming language. It is the result of years of research, development and collaboration between companies and organizations that coordinate the development of Scala with the help of many other people and organizations, and who invest their free time to make it possible. These collaborative efforts have brought us the most notable changes in the language.
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Scala 3 — ?
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Scala 3 — Python 3?
, Scala 3 — Python 3 . , : , Scala 3, Scala 2.13 ( ); Scala; 2 3 Scala, 2 3 Python 3.
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Optional Braces ( )
optional braces , Python. , — , , . , « ». Optional braces — , :
, (, /, );
( , scalafmt), , .)
trait Printer:
def print(msg: String): Unit
class ConsolePrinter extends Printer:
def print(msg: String): Unit = println(msg)
class EmojiPrinter(underlying: Printer) extends Printer:
def print(msg: String): Unit =
val emoji = msg match
case ":)" => ?
case ":D" => ?
case ":|" => ?
case other => other
underlying.print(emoji)
, . Scala 3 end .
class EmojiPrinter(underlying: Printer) extends Printer:
def print(msg: String): Unit =
if msg != null then
val emoji = msg match
case ":)" => ?
case ":D" => ?
case ":|" => ?
case other => other
underlying.print(emoji)
end if
end EmojiPrinter
, , then.
, end , . , , .
end . — , . , « » . , , end :
,
15
4
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Enums
Scala, Java, enum
, . , Scala 3 - , - :
sealed trait Color
case object Red extends Color
case object Green extends Color
case object Blue extends Color
Scala 3, enum
:
enum Color:
case Red, Blue, Green
. , (ADT), . . , Scala 3 ADT enums
:
enum Option[+T]:
case Some(x: T) // extends Option[T] (omitted)
case None // extends Option[Nothing] (omitted)
Scala-enum Java-enum, java.lang.Enum, :
enum Color extends Enum[Color]:
case Red, Blue, Green
println(Color.Green.compareTo(Color.Red)) // 2
, , ADT, enums.
implicit ()
, implicit Scala. , . , implicit , , . , , implicit , , . Scala 3 implicit, . , implicit .
Implicit →
, Scala 3 . implicit . Scala 3 . , .
trait Ord[T]:
def compare(a: T, b: T): Int
given intOrd: Ord[Int] with // with name
def compare(a: Int, b: Int): Int = a - b
given Order[String] with // without name
def compare(a: String, b: String): Int = a.compareTo(b)
Implicit → clauses
( implicit ) . Scala 3 implicit using
. , min
, .
def min[T](a: T, b: T)(using ord: Ord[T]): T =
if ord.compare(a, b) < 0 then a else b
min(4, 2)min(1, 2)(using intOrd)
min("Foo", "Bar")
, .
def printMin[T](a: T, b: T)(using Ord[T]): Unit =
println(min(a, b))
Implicit →
, implicit , , IDE , implicit . Scala 3 .
object A:
class TC
given tc: TC = ???
def f(using TC) = ???
object B:
import A._
import A.given
...
, wildcad (_)
, Scala 3 , . .
object C:
import A.{using, _}
Implicit Conversion → Conversion
, Scala 3, Implicit Conversion
, Implicit Conversion
, . scala.Conversion
, . , scala. Conversion
— . .
abstract class Conversion[-T, +U] extends (T => U):
def apply (x: T): U
, Int Double :
given int2double: Conversion[Int, Double] with
def apply(a: Int): Double = a.toDouble
given Conversion[Int, Double] = _.toDouble
Implicit →
, Implicit
.
case class Image(width: Int, height: Int, data: Array[Byte])
extension (img: Image)
def isSquare: Boolean = img.width == img.height
val image = Image(256, 256, readBytes("image.png"))
println(image.isSquare) // true
, . .
extension [T](list: List[T])
def second: T = list.tail.head
def heads: (T, T) = (list.head, second)
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Scala 3 , — .
— , , . &
. &
: A & B
B & A
. , .
trait Printable[T]:
def print(x: T): Unit
trait Cleanable:
def clean(): Unit
trait Flushable:
def flush(): Unit
def f(x: Printable[String] & Cleanable & Flushable) =
x.print("working on...")
x.flush()
x.clean()
, . , . members ( ). , . members , members .
trait A:
def parent: Option[A]
trait B:
def parent: Option[B]
class C extends A,B:
def parent: Option[A & B] = None
// or
// def parent: Option[A] & Option[B] = Nil
def work(x: A & B) =
val parent:[A & B] = x.parent
// or
// val parent: Option[A] & Option[B] = x.parent
println(parent) // None
work(new C)
, in class C , children member
A B. C — A B, , Option[A] & Option[B]
Option[A & B]
, Option
() .
A | B A B. , , members (), . , members, .
def parseFloat(value: String | Int): Float =
value match
case str: String => str.toFloat
case int: Int => int.floatValue
parseFloat("3.14") // 3.14
parseFloat(42) // 42.0
. , (val
, var
def
) , , ancestor ().
val any = if (cond) 42 else "3.14" // Any
val union: String | Int = if (cond) 42 else "3.14" // String | Int
.
Scala 3 . . , Scala 3.
Case class
, Case class
, new
. Scala 3 new .
Opaque
Opaque- - . Opaque, , , . Opaque- , . , , Opaque-.
Export clauses
Export clauses — members () - . export - ( ) ( ), members .
Scala 2 . , Scala 2, Scala 3 . Scala 3 , . Scala 3.
, Scala 3 . :
(C#P) , .. ;
,
infix
;
- ;
Implicit ;
DelayedInit ;
( = );
XML , ;
,
()
;
.
Scala 3?
, , Scala 3. , , Scala 3 .
, , , . Scala. , , . , Scala 3 , . , , .
Scala 3?
Scala 3 , , , . , , , Scala 3 , Scala 2.13 ( ), , -.
Scala 3?
Scala 3 Scala 2. , Scala 2. Scala 2.13.4, 2020 , , Scala 3. , Scala 3 .
Scala 3 Scala. Scala 3 TASTy Pickle Scala 2.x. Scala 2.13.4 TASTy, , , Enums, Intersection types ( ) . . .
. , , , .
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