Overview of new features in Scala 2.12
At the time of writing, the next planned release of the language is Scala 2.12. From the user and API perspective, Scala 2.12 does not introduce new ground-breaking features. The goal of the 2.12 release is to improve code optimization and make Scala compliant with the Java 8 runtime. Since Scala's primary target is the Java runtime, making Scala compliant with Java 8 runtime will reduce the size of compiled programs and JAR files, better performance and faster compilation. From the user perspective, the major change is that you will have to install the JDK 8 framework instead of JDK 7.
The particular changes in Scala 2.12 worth mentioning are the following:
- In previous versions, traits compiled to a single interface if all of their methods were abstract. If the trait had a concrete method implementation, the compiler generated two class files--one containing the JVM interface, and another class file containing the implementations of the concrete methods. In Scala 2.12, the compiler will generate a single interface file containing the Java 8 default methods. The net effect is reduced code size.
- Previously, each Scala closure was compiled into a separate class. Starting with 2.12, Scala closures are compiled into Java 8-style lambdas. The consequence is reduced code size and potentially better optimizations by the Java 8 runtime.
- Scala compiles into Java bytecodes, which are then interpreted on the Java Virtual Machine. In Scala 2.12, the old compiler backend is replaced with a new implementation that generates bytecode more quickly with a positive impact on compilation speed.
- Scala 2.12 comes with a new optimizer, which is enabled with the
-optcompiler flag. The new optimizer is more aggressive at inlining final methods, does better escape analysis for objects and functions that are created and used in a single method, and does dead code elimination. All this has a positive impact on the performance of Scala programs. - Scala 2.12 allows using lambdas for Single Abstract Method (SAM) types. SAM types are classes or traits that have exactly one abstract method, which is normally implemented by extending the class. Assume that we have a method invocation with an argument whose expected type is a SAM type. If the user passes a lambda, that is, a function literal, instead of a SAM type instance, the 2.12 compiler will automatically convert the function object into an instance of the SAM type.
