I’ve written some basic Android applications in Scala, nothing too epic. Not being a Java programmer I was suggested to use a “treeshake”, I was explained by a friend that this strips out all the unnecessary libraries from the jar files. I have not documented it, but I found that someone else already has: http://chneukirchen.org/blog/archive/2009/04/programming-for-android-with-scala.html … Read more
You have a good point of view on this issue here: The Purpose of Scala’s Type System A Conversation with Martin Odersky, Part III by Bill Venners and Frank Sommers (May 18, 2009) Update (October2009): what follows below has actually been illustrated in this new article by Bill Venners: Abstract Type Members versus Generic Type … Read more
The difference between them is, that a val is executed when it is defined whereas a lazy val is executed when it is accessed the first time. scala> val x = { println(“x”); 15 } x x: Int = 15 scala> lazy val y = { println(“y”); 13 } y: Int = <lazy> scala> x … Read more
This is my working solution using old-style macro annotations. import scala.language.experimental.macros import scala.reflect.macros.blackbox.Context import scala.annotation.StaticAnnotation class fieldable extends StaticAnnotation { def macroTransform(annottees: Any*): Any = macro fieldableMacro.impl } object fieldableMacro { def impl(c: Context)(annottees: c.Expr[Any]*): c.Tree = { import c.universe._ annottees.map(_.tree) match { case (param @ q”case class $className(..$fields)”) :: Nil => { val implicits … Read more
Jim has got this pretty much covered in his blog post, but I’m posting a briefing here for reference. First, let’s see what the Scala Specification tell us. Chapter 3 (types) tell us about Function Types (3.2.9) and Method Types (3.3.1). Chapter 4 (basic declarations) speaks of Value Declaration and Definitions (4.1), Variable Declaration and … Read more
There are a few usages: PartialFunction Remember a PartialFunction[A, B] is a function defined for some subset of the domain A (as specified by the isDefinedAt method). You can “lift” a PartialFunction[A, B] into a Function[A, Option[B]]. That is, a function defined over the whole of A but whose values are of type Option[B] This … Read more
I thought this was asked already, but, if so, the question isn’t apparent in the “related” bar. So, here it is: What is a View Bound? A view bound was a mechanism introduced in Scala to enable the use of some type A as if it were some type B. The typical syntax is this: … Read more
You have three (or so) options to break out of loops. Suppose you want to sum numbers until the total is greater than 1000. You try var sum = 0 for (i <- 0 to 1000) sum += i except you want to stop when (sum > 1000). What to do? There are several options. … Read more
Let me make up for starting some of this confusion by pitching in with some disambiguation. I like to use the analogy to the value level to explain this, as people tend to be more familiar with it. A type constructor is a type that you can apply to type arguments to “construct” a type. … Read more
How about mkString ? theStrings.mkString(“,”) A variant exists in which you can specify a prefix and suffix too. See here for an implementation using foldLeft, which is much more verbose, but perhaps worth looking at for education’s sake.