Indeed – I also find it pretty confusing! Here’s a problem where I have some property which may be a parseable date: def parse(s: String) : Date = new SimpleDateFormat(“yyyy-MM-dd”).parse(s) def parseDate = parse(System.getProperty(“foo.bar”)) type PE = ParseException import scala.util.control.Exception._ val d1 = try { parseDate } catch { case e: PE => new Date … Read more
In 2.8, you import scala.collection.JavaConversions._ and use as a Scala map. Here’s an example (in 2.8.0.RC1): scala> val jmap:java.util.Map[String,String] = new java.util.HashMap[String,String] jmap: java.util.Map[String,String] = {} scala> jmap.put(“Hi”,”there”) res0: String = null scala> jmap.put(“So”,”long”) res1: String = null scala> jmap.put(“Never”,”mind”) res2: String = null scala> import scala.collection.JavaConversions._ import scala.collection.JavaConversions._ scala> jmap.foreach(kv => println(kv._1 + ” … Read more
The problem is that GenericTraversableTemplate is used twice: once for mutable collections (where its type parameter should be invariant), and once for immutable collections (where covariance is invariably king). GenericTraversableTemplate’s typechecks assuming either covariance or invariance for the A type parameter. However, when we inherit it in a mutable trait, we have to pick invariance. … Read more
I’ve been pretty successful with IDEA 9. I’ve briefly tried both Netbeans and Eclipse and wasn’t able to get what I wanted. Eclipse’s code-complete didn’t behave as well as I’d have liked, and I couldn’t find a way to make Netbeans handle Scala scripts; It’d just complain that the file wasn’t a class. To be … Read more
If you want to use the (a, (k, v)) syntax, you need to advise the compiler to use pattern matching. Map(“first”->1, “second”->2).foldLeft(0){ case (a, (k, v)) => a+v } Note that a case statement requires curly braces.
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.”
I have encountered the same scalac error when trying to run a Scala project in Intellij Idea 9.0.2 and I’ve managed to find a solution by chance :). These are the steps I took in creating the project and running it. I have created a Scala project in Intellij Idea 9.0.2 final (it was released … Read more
Since 2.8 Scala has had .toMap, so: val map = seq.map(a => a.key -> a).toMap or if you’re gung ho about avoiding constructing an intermediate sequence of tuples, then in Scala 2.8 through 2.12: val map: Map[Int, A] = seq.map(a => a.key -> a)(collection.breakOut) or in Scala 2.13 and 3 (which don’t have breakOut, but … Read more
Starting Scala 2.13, the standard library provides a dedicated resource management utility: Using. It can be used in this case with scala.io.Source as it extends AutoCloseable in order to read from a file and, no matter what, close the file resource afterwards: import scala.util.Using import scala.io.Source Using(Source.fromFile(“file.txt”)) { source => source.mkString } // scala.util.Try[String] = … Read more
Type Constructors as Type Parameters M is a type parameter to one of Scalaz’s main pimps, MA, that represents the Type Constructor (aka Higher Kinded Type) of the pimped value. This type constructor is used to look up the appropriate instances of Functor and Apply, which are implicit requirements to the method <**>. trait MA[M[_], … Read more