nelanka

Scala Brown Bag Lunch Series

Day 1

Introduction to Developing in Scala

• Setup of tool chain
• Value Types
• Simple functions

Day 2

nelanka

trait Foo[T] {
  def foo(t: T): String
}

// Creates an implicit function that uses an implicit Foo[T] (evidence)
implicit def foo[T](t: T)(implicit ev: Foo[T]): String = ev.foo(t)

// Or using context bounds (choose one or the other depending on usage of the implicit evidence)
implicit def foo[T : Foo](t: T): String = implicitly[Foo[T]].foo(t)

nelanka

Add rx things together and log stuff:
(consumer.stream1 ++ consumer.stream2 ++ consumer.stream3).subscribe(event => logger.info("Received event " + event))

Filter out messages:
consumer.stream1.filter(_.isEnabled != true).subscribe(event => map.remove(event.id))

It’s kinda handy that rx streams are basically infinite lists that you can apply all scala magical collection incantations to.

nelanka

for (ln <- io.Source.stdin.getLines()) println(ln)

Iterator.continually(StdIn.readLine()).takeWhile(_.nonEmpty).foreach(line => println("read " + line))

Observable.from(Iterator.continually(StdIn.readLine()).toIterable).subscribe(line => println("read " + line))

nelanka

def fib(n: Int): Stream[Int] = n match {
  case 0 ⇒ 0 #:: fib(1)
  case 1 ⇒ 1 #:: fib(2)
  case _ ⇒ (fib(n - 1).head + fib(n - 2).head) #:: fib(n + 1)
}

fib(0) take 10 foreach println

// From http://www.scala-lang.org/api/current/#scala.collection.immutable.Stream
val fibs: Stream[BigInt] = BigInt(0) #:: BigInt(1) #:: fibs.zip(fibs.tail).map { n => n._1 + n._2 }

nelanka

import org.scalacheck.Prop.BooleanOperators
import org.scalacheck.{Arbitrary, Gen}
import org.scalatest.prop.GeneratorDrivenPropertyChecks
import org.scalatest.{FreeSpec, Matchers}

/**
 * Some example usages of the (Scala Check)[http://scalacheck.org] library
 *
 * References:
 * (Scala Check User Guide)[https://github.com/rickynils/scalacheck/wiki/User-Guide]

nelanka

  object OptionToOr {
    implicit class PimpedOption[T](opt: Option[T]) {
      def orError(error: String): T Or Every[String] = opt match {
        case Some(value) => Good(value)
        case None => Bad(One(error))
      }    
    }
  }

nelanka

Excluding files from git's changeset

I often find myself leaving out a change set of local changes that I don’t want to check in. In Idea, you can add them to a separate change list of local changes and ignore them from commits. On the command line, you can do a local ignore/untrack of a file, whithout using .gitignore. Useful if your .gitignore is also itself checked into git.

Change the file(s) to be untracked:

nelanka@hydra:/Projects/booking> git status
On branch master
Your branch is up-to-date with 'origin/master'.

nelanka

" ~/.vim/filetype.vim

au BufNewFile,BufRead *.gradle setf groovy

nelanka

*.class
*.log

# mine
.idea
build
target
logs
.gradle
data