kpmeen

body { background: #222; color: #e6e6e6; }

a { color: #949494; }

a:link, a:visited { color: #949494; }

a:hover, a:active, a:focus { color: #c7c7c7; }

hr { border-bottom: 1px solid #424242; border-top: 1px solid #222; }

kpmeen

introduction

ScalaCheck 1.14.0 was just released with support for deterministic testing using seeds. Some folks have asked for examples, so I wanted to produce a Gist to help people use this feature.

simple example

These examples will assume the following imports:

kpmeen

import scala.util.Try

object PathSerializer {

  trait SerDe[A] {
    // By using a path dependent type, we can be sure can deserialize without wrapping in Try
    type Serialized
    def ser(a: A): Serialized
    def deser(s: Serialized): A
    // If we convert to a generic type, in this case String, we forget if we can really deserialize

kpmeen

import java.util.concurrent.ExecutionException

import scala.concurrent.{ExecutionContext, ExecutionContextExecutor, Future}
import scala.concurrent.forkjoin.ForkJoinPool
import scala.util.Failure

object BlockingExecutor {

  private[this] val threadCount = 5

kpmeen

apiVersion: extensions/v1beta1
kind: PodSecurityPolicy
metadata:
  name: restricted
  annotations:
    seccomp.security.alpha.kubernetes.io/allowedProfileNames: 'docker/default'
    apparmor.security.beta.kubernetes.io/allowedProfileNames: 'runtime/default'
    seccomp.security.alpha.kubernetes.io/defaultProfileName:  'docker/default'
    apparmor.security.beta.kubernetes.io/defaultProfileName:  'runtime/default'
spec:

kpmeen

val (recycleQueue, recycleSource) =
  Source
    .queue[SoilStateReading](100, OverflowStrategy.dropTail)
    .prefixAndTail(0)
    .map(_._2)
    .toMat(Sink.head)(Keep.both)
    .run()
StreamConverters.fromInputStream(() => this.getClass.getClassLoader.getResourceAsStream("sensors.log"))
  .via(SoilStateReading.csvParser)
  .merge(Source.fromFutureSource(recycleSource))

kpmeen

import play.api.libs.json.Json

object Main{
  def main(args: Array[String]): Unit = {
    println(
      Json.prettyPrint(
        Json.toJson(Seq("Hello", "World", "Cow"))
      )
    )
  }

kpmeen

// Build Scala source code
val tree = q"""
object Test {  
  val a = 2 + 5
  def f(b: String) = { b + a.toString }
}
"""
val src = List(TreeNode(tree))

// Build Scala target code

kpmeen

Latency Comparison Numbers

Note: "Forked" from Latency Numbers Every Programmer Should Know

Event	Nanoseconds	Microseconds	Milliseconds	Comparison
L1 cache reference	0.5	-	-	-
Branch mispredict	5.0	-	-	-
L2 cache reference	7.0	-	-	14x L1 cache
Mutex lock/unlock	25.0	-	-	-

kpmeen

How to GPG as a Scala OSS Maintainer

tl;dr Generate a GPG key pair (exercising appropriate paranoia). Send it to key servers. Create a Keybase account with the public part of that key. Use your keypair to sign git tags and SBT artifacts.

GPG is probably one of the least understood day-to-day pieces of software in the modern developer's toolshed. It's certainly the least understood of the important pieces of software (literally no one cares that you can't remember grep's regex variant), and this is a testament to the mightily terrible user interface it exposes to its otherwise extremely simple functionality. It's almost like cryptographers think that part of the security comes from the fact that bad guys can't figure it out any more than the good guys can.

Anyway, GPG is important for open source in particular because of one specific feature of public/private key cryptography: signing. Any published software should be signed by the developer (or company) who published it. Ideally, consu