scala

Using GitHub projects as Scala library dependencies with sbt and sbteclipse

Okay, this is pretty cool. With sbt, you can magically refer to dependencies that are set up as GitHub projects, and those projects don't need to have a jar file, they can just be a source code library. This means you can save your Scala libraries as source code to GitHub (like you normally would), then pull them into your other Scala projects simply by referencing them in your build.sbt file.

Assuming you're comfortable with sbt, here's a quick six-step example that shows how to pull a GitHub library into a simple Scala project:

By Alvin Alexander on November 1, 2012

Making Twitter web service calls concurrently with Akka Futures

While I was working on improving how Sarah gets information from Twitter and other sources, I decided to take some of that code and hack together this example. It shows how to make three Twitter web service requests concurrently -- and then wait for ther results before moving on -- with Akka Futures.

Before sharing the entire class, the cool Akka Futures stuff is in these lines of code:

By Alvin Alexander on February 26, 2013

A Scala implicit method argument and field example

UPDATE: This example shows how to create an implicit method in Scala 2.9 or older. You can use a slightly simpler approach with Scala 2.10 and newer, which I've documented in this Scala 2.10 implicit class example.

I'm not going to do much writing here today, but instead I'll just demonstrate how an implicit method argument works with implicit fields in Scala. Without any further ado, here's some code:

By Alvin Alexander on February 18, 2013

Scala - A simple working Akka Futures example

Akka Futures FAQ: Can you share a simple example that shows how to use an Akka Future?

Sure. To fix a problem in my Sarah application I needed to be able to run some operations concurrently. After digging through the Akka Actors documentation I found that you can run simple operations as a Future, almost as easily as this:

By Alvin Alexander on February 26, 2013

An Akka actors 'ask' example - ask, future, await, timeout, duration, and all that

Akka actor ask FAQ: Can you share an example that shows how one Akka actor can ask another actor for information?

Sure. Here's a quick example to demonstrate how one Akka actor can ask another Akka actor for some information and wait for a reply. When using this "ask" functionality, you can either use the "ask" method, or the "?" operator, and I've shown both approaches below.

By Alvin Alexander on February 26, 2013

Making your Scala code more concise (and your intent more clear)

I was trying to write some code last night while I was very tired, and while the code itself isn't difficult in any way, the thought process I went through demonstrates how your code can become more concise as your understanding of Scala evolves, so I thought I'd share the experience here.

While working on my Sarah application, I was rewriting the Brain class, and I started off writing a method that looked like this:

By Alvin Alexander on November 1, 2012

Using puts or echo instead of println in Scala

As my mind was wandering off earlier today, I started to wonder what it would take to create a Ruby puts or PHP echo statement in Scala. (For some reason my brain can never type "println", and puts or echo are much easier to type.)

One simple way to mimic a puts or echo operator is to use Scala's ability to rename things on import:

By Alvin Alexander on November 1, 2012

How to stop an Akka actor (and shutdown the Akka system)

Akka actor FAQ: How do you stop an Akka actor?

I don't have time this morning to write my usual tutorial, so in short, if you want to stop an Akka actor, use code like this from inside your actor's receive method:

context.stop(self)

Or, if you want to shut down the Akka system, use the following code, again from inside the receive method of one of your actors:

By Alvin Alexander on February 26, 2013

Scala SBT tool history commands

When you're using the SBT tool with your Scala projects, it can be helpful to list your "sbt history", the history of your SBT commands. Courtesy of the SBT tool itself, here are the history commands you can use from the sbt command line:

By Alvin Alexander on November 1, 2012

Does Scala have a String variable substitution syntax like Ruby?

Scala FAQ: Does Scala have a String variable substitution syntax like Ruby?

UPDATE: If you're using Scala 2.10 or newer, see my new String interpolation in Scala 2.10 (embedding variables in strings) tutorial. If you're using Scala 2.9.x or older, continue with this article.

By Alvin Alexander on January 23, 2013

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