scala

There are no ++ or -- operators in Scala (use += or -=)

In Scala there are no ++ or -- operators. You should instead use the += and -= operators, as shown below. First the += operator:

scala> var i = 1
i: Int = 1

scala> i++
<console>:9: error: value ++ is not a member of Int
              i++
               ^

scala> i += 1

scala> println(i)
2

Next the -= operator:

Submitted by alvin on May 19, 2012 - 6:47pm

How to execute (exec) external system commands in Scala

When it comes to executing external system commands, Scala is a dramatic improvement over Java. The operators Scala makes available are much more like Perl or Ruby, and the operators themselves are consistent with traditional shell commands, and are therefore easy to remember. Let's take a look at a few examples.

Executing system commands and getting their status code (exit code)

It's very easy to run external system commands in Scala. You just need one import statement, and then you run your command as shown below with the "!" operator:

Submitted by alvin on May 19, 2012 - 4:36pm

How to enter multiline commands (statements) into the Scala REPL

When you want to test a multiline command/statement in the Scala REPL, you can easily run into a problem where the REPL gets confused, or more accurately, it attempts to evaluate your statement too early.

As a simple example of this, imagine that you want to test the Scala "if" statement syntax. You begin typing your if statement normally, but when you hit [Enter] after your second line, you'll see that everything blows up:

Submitted by alvin on May 18, 2012 - 2:44pm

Scala shell scripts and the command line: Prompting the user, and reading input

A great thing about Scala is that not only is it scalable, it was also created to help you work on small tasks, including being useful in simple shell scripts. This includes small shell script tasks like prompting a user interactively from a shell script, and reading their input.

You can prompt users with print commands like println and print, and you can read their input with all of these methods that are available on the Console class:

Submitted by alvin on May 17, 2012 - 3:02pm

Scala REPL - How to show more methods on a class/object in the REPL

When you're working in the Scala REPL and want to see what methods are available on a class/object, you can create an instance of an object, follow that with the "." character, and then press the [Tab] key. This process, known as "tab completion" in the REPL, gives you a preliminary list of methods that can be called on the object.

Here's what this looks like when we try it on an Int object:

Submitted by alvin on May 16, 2012 - 3:45pm

How to exit a Scala Actor (exit, quit, or terminate an Actor)

While working with a Scala Actor last night, I came across a situation where I wanted to be able to manually tell the Actor to quit/die/terminate.

It looks like the proper way to exit a Scala Actor is pretty simple:

Submitted by alvin on May 15, 2012 - 8:29pm

How to run ScalaTest unit tests in Eclipse

I do a lot of work from the command line with Ant builds and similar things, but there are times I like to do things through Eclipse. Today I wanted to run my ScalaTest unit tests in Eclipse, and found this to be a straightforward task.

Besides Scala, Eclipse, and an Eclipse project, you'll need:

Submitted by alvin on May 15, 2012 - 8:21pm

A Scala String to Int conversion example

If you need to convert a String to Int in Scala, just use the toInt method which is available on String objects, like this:

scala> val i = "1".toInt
i: Int = 1

As you can see, I just cast a String (the string "1") to an Int object using the toInt method on the String.

Note that this can fail just like it does in Java, with a NumberFormatException, like this:

Submitted by alvin on May 15, 2012 - 8:12pm

How to show Scala String and StringOps methods in the REPL

Just a quick note here today on how to show methods from the String class in the Scala REPL, as well as methods from the StringOps class, which aren't seen as easily.

First, if you've used tab completion in the REPL, you may already know that you can show many String class methods in the REPL. If you hit the [Tab] key once you'll see a short list of String methods:

Submitted by alvin on May 15, 2012 - 2:57pm

Make your Scala shell scripts run faster with the "savecompiled" argument

I was just reading the Scala man page, looking for something else, when I ran across this tip on how to speed up the execution of Scala shell scripts, using the savecompiled flag of the scala command:

Submitted by alvin on May 14, 2012 - 3:09pm