It “splats”1 the sequence. Look at the constructor signature new Elem(prefix: String, label: String, attributes: MetaData, scope: NamespaceBinding, child: Node*) which is called as new Elem(prefix, label, attributes, scope, child1, child2, … childN) but here there is only a sequence, not child1, child2, etc. so this allows the result sequence to be used as the … Read more
case classcomes with a copy method that is dedicated exactly to this usage: val newPersona = existingPersona.copy(sentMessages = existingPersona.sentMessages + newMessage)
Use parentheses: data(2) But you don’t really want to do that with lists very often, since linked lists take time to traverse. If you want to index into a collection, use Vector (immutable) or ArrayBuffer (mutable) or possibly Array (which is just a Java array, except again you index into it with (i) instead of … Read more
Method def even evaluates on call and creates new function every time (new instance of Function1). def even: Int => Boolean = _ % 2 == 0 even eq even //Boolean = false val even: Int => Boolean = _ % 2 == 0 even eq even //Boolean = true With def you can get … Read more
Here’s one difference – case objects extend the Serializable trait, so they can be serialized. Regular objects cannot by default: scala> object A defined module A scala> case object B defined module B scala> import java.io._ import java.io._ scala> val bos = new ByteArrayOutputStream bos: java.io.ByteArrayOutputStream = scala> val oos = new ObjectOutputStream(bos) oos: java.io.ObjectOutputStream … Read more
One big difference is that Enumerations come with support for instantiating them from some name String. For example: object Currency extends Enumeration { val GBP = Value(“GBP”) val EUR = Value(“EUR”) //etc. } Then you can do: val ccy = Currency.withName(“EUR”) This is useful when wishing to persist enumerations (for example, to a database) or … Read more
[*] RDDs extend the Serialisable interface, so this is not what’s causing your task to fail. Now this doesn’t mean that you can serialise an RDD with Spark and avoid NotSerializableException Spark is a distributed computing engine and its main abstraction is a resilient distributed dataset (RDD), which can be viewed as a distributed collection. … Read more
List(1,2,3) :+ 4 Results in List[Int] = List(1, 2, 3, 4) Note that this operation has a complexity of O(n). If you need this operation frequently, or for long lists, consider using another data type (e.g. a ListBuffer).
The example you have given only uses call-by-value, so I will give a new, simpler, example that shows the difference. First, let’s assume we have a function with a side-effect. This function prints something out and then returns an Int. def something() = { println(“calling something”) 1 // return value } Now we are going … Read more
For most cases you do not need an external parser. Scala’s pattern matching allows consuming args in a functional style. For example: object MmlAlnApp { val usage = “”” Usage: mmlaln [–min-size num] [–max-size num] filename “”” def main(args: Array[String]) { if (args.length == 0) println(usage) val arglist = args.toList type OptionMap = Map[Symbol, Any] … Read more