Resources in Scala work exactly as they do in Java. It is best to follow the Java best practices and put all resources in src/main/resources and src/test/resources. Example folder structure: testing_styles/ ├── build.sbt ├── src │ └── main │ ├── resources │ │ └── readme.txt Scala 2.12.x && 2.13.x reading a resource To read resources … Read more
First, they are all non-strict. That has a particular mathematical meaning related to functions, but, basically, means they are computed on-demand instead of in advance. Stream is a lazy list indeed. In fact, in Scala, a Stream is a List whose tail is a lazy val. Once computed, a value stays computed and is reused. … Read more
From the LinkedHashMap Scaladoc page: “This class implements mutable maps using a hashtable. The iterator and all traversal methods of this class visit elements in the order they were inserted.”
You could use a mutable.Map[TupleN[A1, A2, …, AN], R] , or if memory is a concern, a WeakHashMap[1]. The definitions below (built on the memoization code from michid’s blog) allow you to easily memoize functions with multiple arguments. For example: import Memoize._ def reallySlowFn(i: Int, s: String): Int = { Thread.sleep(3000) i + s.length } … Read more
From the Scala docs: Note: the difference between c filter p and c withFilter p is that the former creates a new collection, whereas the latter only restricts the domain of subsequent map, flatMap, foreach, and withFilter operations. So filter will take the original collection and produce a new collection, but withFilter will non-strictly (i.e. … Read more
Foreword There’s a 2.8 collection walk-through by Martin Odersky which should probably be your first reference. It has been supplemented as well with architectural notes, which will be of particular interest to those who want to design their own collections. The rest of this answer was written way before any such thing existed (in fact, … Read more
It’s entirely possible to use JavaConverters in Java code—there are just a couple of additional hoops to jump through: import java.util.HashMap; import scala.Predef; import scala.Tuple2; import scala.collection.JavaConverters; import scala.collection.immutable.Map; public class ToScalaExample { public static <A, B> Map<A, B> toScalaMap(HashMap<A, B> m) { return JavaConverters.mapAsScalaMapConverter(m).asScala().toMap( Predef.<Tuple2<A, B>>conforms() ); } public static HashMap<String, String> example() { … Read more
a: A is type ascription; see What is the purpose of type ascriptions in Scala? : _* is a special instance of type ascription which tells the compiler to treat a single argument of a sequence type as a variable argument sequence, i.e. varargs. It is completely valid to create a Queue using Queue.apply that … Read more
As a general rule, default to using Vector. It’s faster than List for almost everything and more memory-efficient for larger-than-trivial sized sequences. See this documentation of the relative performance of Vector compared to the other collections. There are some downsides to going with Vector. Specifically: Updates at the head are slower than List (though not … Read more
EDIT: Java Conversions got @deprecated in Scala 2.13.0. Use scala.jdk.CollectionConverters instead. JavaConversions provide a series of implicit methods that convert between a Java collection and the closest corresponding Scala collection, and vice versa. This is done by creating wrappers that implement either the Scala interface and forward the calls to the underlying Java collection, or … Read more