How to filter None’s out of List[Option]?
If you want to get rid of the options at the same time, you can use flatten: scala> someList.flatten res0: List[String] = List(Hello, Goodbye)
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Why does pattern matching in Scala not work with variables?
What you’re looking for is a stable identifier. In Scala, these must either start with an uppercase letter, or be surrounded by backticks. Both of these would be solutions to your problem: def mMatch(s: String) = { val target: String = “a” s match { case `target` => println(“It was” + target) case _ => … Read more
SBT stop run without exiting
From sbt version 0.13.5 you can add to your build.sbt cancelable in Global := true It is defined as “Enables (true) or disables (false) the ability to interrupt task execution with CTRL+C.” in the Keys definition If you are using Scala 2.12.7+ you can also cancel the compilation with CTRL+C. Reference https://github.com/scala/scala/pull/6479 There are some … Read more
Cleaner way to update nested structures
Funny that no one added lenses, since they were MADE for this kind of stuff. So, here is a CS background paper on it, here is a blog which touch briefly on lenses use in Scala, here is a lenses implementation for Scalaz and here is some code using it, which looks surprisingly like your … Read more
In Scala, what exactly does ‘val a: A = _’ (underscore) mean?
val a: A = _ is a compile error. For example: scala> val a: String = _ <console>:1: error: unbound placeholder parameter val a: String = _ ^ What does work is var a: A = _ (note var instead of val). As Chuck says in his answer, this initialises the variable to a default … Read more
How to read files from resources folder in Scala?
Resources in Scala work exactly as they do in Java. It is best to follow the Java best practices and put all resources in src/main/resources and src/test/resources. Example folder structure: testing_styles/ ├── build.sbt ├── src │ └── main │ ├── resources │ │ └── readme.txt Scala 2.12.x && 2.13.x reading a resource To read resources … Read more
Scala downwards or decreasing for loop?
scala> 10 to 1 by -1 res1: scala.collection.immutable.Range = Range(10, 9, 8, 7, 6, 5, 4, 3, 2, 1)
What are some compelling use cases for dependent method types?
More or less any use of member (ie. nested) types can give rise to a need for dependent method types. In particular, I maintain that without dependent method types the classic cake pattern is closer to being an anti-pattern. So what’s the problem? Nested types in Scala are dependent on their enclosing instance. Consequently, in … Read more
How to force IntelliJ IDEA to reload dependencies from build.sbt after they changed?
You can force SBT to reload changes: Open SBT toolwindow (on the right side of IDE) and press refresh button. If you use auto-import feature you need to save your file to force auto-refresh.
What are the key differences between Scala and Groovy? [closed]
They’re both object oriented languages for the JVM that have lambdas and closures and interoperate with Java. Other than that, they’re extremely different. Groovy is a “dynamic” language in not only the sense that it is dynamically typed but that it supports dynamic meta-programming. Scala is a “static” language in that it is statically typed … Read more