What’s new

• Collections overhaul
• Future is faster and more robust
• Language: literal types, partial unification, more
• Compiler: 5-10% faster

Read more

What’s deprecated

Procedure syntax

def m() { ... }

  ↓

def m(): Unit = { ... }

What’s deprecated

Unicode arrows

What’s deprecated

Postfix operators

xs size

  ↓

xs.size

Collections overhaul

For simplicity, performance and safety

• Simpler signatures:
  CanBuildFrom
• Simpler hierarchy:
  Traversable, TraversableOnce

Collections overhaul

scala.Seq is now immutable! 🎉

Collections overhaul

Deprecated /: and :\

(use foldLeft and foldRight)

Collections overhaul

much, much more

Java interop moved

more about that later

Using

Using(new BufferedReader(new FileReader("file"))) { reader =>
  // do stuff
}

reader.close() called automatically

tap

Useful for debugging

val result = ???
println(result)
result

↓

import scala.util.chaining._

result.tap(println)

toIntOption

"12".toIntOption   → Some(12)
"nope".toIntOption → None

Either

.right is deprecated

Either is now right-biased

Our application

• Uses Slick
• Uses ScalaTest
• Maven build 😢
• Lots of linting
• Scoverage

Build

Build

Recommended flags for 2.12 by tpolecat

Not all of them work

Build

• -Ywarn-inaccessible → -Xlint:inaccessible
  Inaccessible types in method signatures
• -Yno-adapted-args
  Do not adapt an argument list (either by inserting () or creating a tuple) to match the receiver

Build

<artifactId>scalafmt-core_${scala.version}</artifactId>

  ↓

<artifactId>scalafmt-core_2.12</artifactId>

Scala-fmt is not available for 2.13 yet

But it doesn’t matter

Code

Code

array.map(...)

  ↓

array.toSeq.map(...)

Arrays are mutable

map should not mutate in-place

Code

import scala.collection.immutable.Seq

  ↓

nothing

🎉

Code

import scala.collection.JavaConverters._

  ↓

import scala.jdk.CollectionConverters._

Java interop has moved

Code

myMap.filterKeys(...)
myMap.mapValues(...)

  ↓

myMap.view.filterKeys(...)
myMap.view.mapValues(...)

They are implemented as views; this makes that explicit

Strict versions may come later

Code

Stream.continually(...)

  ↓

LazyList.continually(...)

Stream is deprecated because it was not fully lazy

Scala-Maven-Plugin

Did you update?

ScalaTest

≥ 3.0.8

ScalaTest

import org.scalatest.prop.Checkers

  ↓

import org.scalatestplus.scalacheck.Checkers

ScalaCheck related classes have moved to ScalaTestPlus

ScalaTest

Remove EitherValues trait

e.right.value

  ↓

e.toOption.value

Because Either.right is deprecated

Slick

≥ 3.3.2

Slick

• Now supports java.time
• Requires changes if you already have mappings for these types!
• Especially on MySql/MariaDB, where Slick uses VARCHAR instead of TIMESTAMP

Scoverage

≥ 1.4.0

Scoverage

scoverage-maven-plugin 1.4.0 does not exist 😢

Fork this Pull Request

Scoverage

Measures differently: may need to adjust thresholds

WartRemover

WartRemover

Any

Now unusable due to so many false positives

WartRemover

StringPlusAny

Now also applies to string-interpolation!

Also, any2stringadd is now deprecated in Scala anyway

Random dependency hell

Transitive dependencies may or may not be compatible

<exclusions>
  <!-- pulls in Jackson for Scala 2.12 instead of 2.13,
       so we have to suppress here -->
  <exclusion>
      <groupId>com.fasterxml.jackson.module</groupId>
      <artifactId>jackson-module-scala_2.12</artifactId>
  </exclusion>
</exclusions>