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Scala extractors infix sample with Rational numbers

I keep coming back to the awesome introductory material on Scala put together by Daniel Westheide. One of the examples that he provides for extractors using an infix operation pattern is the Streams API – val xs = 58 #:: 43 #:: 93 #:: Stream.empty xs match {   case first #:: second #:: _ => first - second   ...

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Clojure web development – state of the art – part 2

This is part 2 of my “Clojure web development” series. You can discuss first part on this reddit thread. After reading the comments I must explain two assumptions I had writing this series: Keep things easy to understand for people from outside Clojure land, especially Java devs. That’s why I use REST/JSON in favor of transit and component as a ...

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Akka Typed: First steps with typed actors in Scala

With the [release of Akka 2.4.0| http://akka.io/news/] a couple of weeks ago the experimental Akka Typed module was added. With Akka Typed it is possible to create and interact with Actors in a type safe manner. So instead of just sending messages to an untyped Actor, with Akka Typed we can add compile time type checking to our Actor interactions. ...

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Testing Asynchronous Code

Asynchronous code is hard. Everyone knows that. Writing asynchronous tests is even harder. Recently I fixed a flaky test and I want to share some thoughts about writing asynchronous tests. In this post we explore a common problem with asynchronous tests—how to force a test to take a specific ordering between threads, and forcing some operations by some threads to ...

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Integration testing with Gradle

Unit testing works automatically using Gradle, but if you would like to have a separate set of integration tests you need to do a small exercise. Actually they don’t have to be integration tests at all. This guide shows you how to configure Gradle to use any kind of tests and run them independently from others. I will use Scala ...

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Listen to notifications from Postgresql with Scala

In the past I’ve written a couple of articles (Building a REST service in Scala with Akka HTTP, Akka Streams and reactive mongo and ReactiveMongo with Akka, Scala and websockets) which used MongoDB to push updates directly from the database to a Scala application. This is a very nice feature if you just want to subscribe your application to a ...

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Avoid NullPointerException: Safe Navigation with Groovy

We know it’s all too common in Java to get a NullPointerException when we use an object reference which is null. This happens when our code tries to access a method or field of an object, or element of an array when there’s no instance present – e.g. it refers to null. class Animal { String name Animal parent } ...

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Scala typeclass explained: Implement a String.read function

In this short article I’d like to explain how you can use the typeclass pattern in Scala to implement adhoc polymorphism. We won’t go into too much theoretical details in this article, the main thing I want to show you is how easy is really is to create a flexible extensible model without tying your domain model to specific implementation ...

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