Implicit classes effectively only add new methods (or traits), and they are only ever used when these added methods are called (or the implicit class is used explicitly, but this rarely happens in practice). Implicit conversions to existing types, on the other hand, can be invoked with less visibility to the programmer.
PS: I wonder why Play Iteratees library has not been choosed by Martin Odersky for his course since Play is in the Typesafe stack. Does it mean Martin prefers RxScala over Play Iteratees? I’ll answer this. The decision of which streaming API’s to push/teach is not one that has been made just by Martin, but … Read more
Scala’s exception handling works by passing any exceptions to an anonymous catch function. The catch function works by pattern matching the caught exception and, if it doesn’t match it will pass the exception up. The catch function is optional, if it’s omitted then the exception is passed straight up. So essentially try { exceptionThrowingFunction() } … Read more
The reason is that the base class method is abstract abstract class IntQueue { def get(): Int def put(x: Int) } If you were to not put abstract on the trait you end up with the explanation you were seeking: trait Doubling extends IntQueue { override def put(x: Int) { super.put(2 * x) } } … Read more
Mixin has been the classic way to introduce AOP in Scala (as in “AOP-style Mixin Composition Stacks in Scala” from Jonas Bonér). But I know only of “Method Proxy-Based AOP in Scala” (Daniel Spiewak — also here on SO — and Tian Zhao) as an advanced AOP implementation in Scala (source code here). Our technique … Read more
Difference between df.select(“foo”) and df.select($”foo”) is signature. The former one takes at least one String, the later one zero or more Columns. There is no practical difference beyond that. myDataSet.map(foo.someVal) type checks, but as any Dataset operation uses RDD of objects, and compared to DataFrame operations, there is a significant overhead. Let’s take a look … Read more
When I was trying something similar I came to the conclusion that it’s better to break it on 2 parts: Use Play as a backend you interact with via Ajax calls Store the Angular templates in Play public folder (something like /public/angular/) and use the default AngularJs way to map the templates I know it … Read more
You have two options: 1. Create a singleton object with a lazy val representing the data: object WekaModel { lazy val data = { // initialize data here. This will only happen once per JVM process } } Then, you can use the lazy val in your map function. The lazy val ensures that each … Read more
The answer here is a combination of items: (a) create a brand new Scala project (as suggested by @lhuang) and (b) when running a script, you need to go into the Run Configuration and remove the Make step (as mentioned in the ‘related’ SOF question). This shows rough edges with Intellij and its scala plugin. … Read more
The Enumeration values are instance of the Val class. This class can be extended and a factory method can be added. object My extends Enumeration { val A = Value(“name”, “x”) val B = Value(“other”, “y”) class MyVal(name: String, val x : String) extends Val(nextId, name) protected final def Value(name: String, x : String): MyVal … Read more