Scala 3 revolutionizes the language for a better experience for developers

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Scala 3 has overhauled the language for a better developer experience

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Jun 24, 2021 3 min read

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  • Carsten Syertz

Eight years, 28,000 commits, 7,400 pull requests, and 4,100 closed questions later, Scala 3.0 has been released, providing a “complete overhaul of the Scala language,” including new features, an update to the syntax and type system, and new tools for metaprogramming. Scala Compatibility Reference hailed release 3 as a “game changer” [……] It will greatly improve the everyday experience of every Scala programmer. Scala 3 is binary compatible with Scala 2.13, but not completely source compatible. The new Dotty compiler can automatically migrate old code and report any legacy issues.

Scala 3.0’s new syntax is much more concise. The new keyword is now optional (similar to the feature Google introduced in Dart 2.0), as are the parentheses in control structure expressions. Some of the curly braces that occur can be replaced with source indentation, a well-known feature of Python.

New language features allow developers to express their intentions directly with questionable context abstractions: Using clauses and Given instances simplify context parameters, extension methods are first-class language citizens, and implicit transformations are now built as instances of the Scala.conversion class.

The type system has also been improved, such as simplified enumerations; Opaque types that hide implementation details Provide A | B and A & B respectively crossover and joint type of grammar; New dependent function types, whose results depend on the parameters of the function; And lambdas, the built-in type that used to require a compiler plug-in in Scala 2.

The enumeration syntax in Scala 2 is verbose. Take a look at the following example.

sealed trait Direction 
case object East extends Direction
case object West extends Direction
Copy the code

Scala 3 introduces a more concise syntax.

enum Direction:
   case: East.West
Copy the code

Functional programming has been simplified with the redesign of context abstractions and changes to the type system. Object-oriented development has also been improved, with new features including: Traits accept parameters and is declared (transparent) (https://dotty.epfl.ch/docs/reference/other-new-features/transparent-traits.html); An open modifier that explicitly marks the class as an open extension; In the spirit of encouraging decorators to design patterns in favor of composition over inheritance, define aliases for selected members of the object by providing an export clause.

Macros, first introduced in Scala 2.10, are an experimental feature. Scala 3 introduces a set of metaprogramming tools that feature inline methods to improve application performance; Compile-time operations that can be used with inline methods; Reference code blocks to build and analyze code; And the reflection API to provide a view of the typed abstract syntax tree including the TASTy file. The Scala 3 macro is designed to ensure stability and will be compatible with future versions of Scala. However, under this new metaprogramming model, Scala 2.13 macros will need to be rewritten. In addition, many Scala 2 [scaladoc] (https://docs.scala-lang.org/style/scaladoc.html) Settings have changed, so that the parameters in the Scala 3 standardization.

New compiler options such as -xignore-scala2-macros ignore compiler errors in code that calls Scala 2 macros; -print-tasty prints the original tasty file; -no-indent will execute classical syntax, and these are just some of the many new options for compiling code. The Migration guide details the migration to Scala 3 and includes a tutorial on porting a complete Scala 2.13 project to Scala 3.

A Scala 3.0 application can still use a Scala 2.13 library, even with macros — unless a non-working macro breaks the library. Vice versa, for example, a Scala 2.13 application can use Scala 3.0 libraries. The Scala Library Index, also known as Scaladex, lists which libraries are ready for Scala 3.0.

However, these changes come at a cost, as some Scala 2.13 source code is incompatible with Scala 3.0. Fortunately, the new compiler includes a migration mode that automatically migrates Scala 2 code to Scala 3 and reports any remaining problems that need to be fixed manually.

More information about Scala 3 can be found in the new Content section of the site.

The easiest way to get started with Scala 3.0 is to use Scastie, Scala’s online IDE, which allows you to write and execute code directly from the browser. It also shows how to run a “Hello, world “program.

Five weeks after its release, the Documentation and book for Scala 3.0 are not yet complete, and we encourage the Scala community to contribute.

After 3.0, new Scala releases are expected every six weeks. Developers can expect the next release at the end of June 2021.

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