a: A is type ascription; see What is the purpose of type ascriptions in Scala? : _* is a special instance of type ascription which tells the compiler to treat a single argument of a sequence type as a variable argument sequence, i.e. varargs. It is completely valid to create a Queue using Queue.apply that … Read more
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
First, they are all non-strict. That has a particular mathematical meaning related to functions, but, basically, means they are computed on-demand instead of in advance. Stream is a lazy list indeed. In fact, in Scala, a Stream is a List whose tail is a lazy val. Once computed, a value stays computed and is reused. … Read more
Immutable Structures The Scala List is an immutable recursive data structure which is such a fundamental structure in Scala, that you should (probably) be using it much more than an Array (which is actually mutable – the immutable analog of Array is IndexedSeq). If you are coming from a Java background, then the obvious parallel … Read more
You can use c map (t => t.getP -> t) toMap but be aware that this needs 2 traversals.
In general, all 6 fold functions apply a binary operator to each element of a collection. The result of each step is passed on to the next step (as input to one of the binary operator’s two arguments). This way we can cumulate a result. reduceLeft and reduceRight cumulate a single result. foldLeft and foldRight … Read more
EDIT: Java Conversions got @deprecated in Scala 2.13.0. Use scala.jdk.CollectionConverters instead. JavaConversions provide a series of implicit methods that convert between a Java collection and the closest corresponding Scala collection, and vice versa. This is done by creating wrappers that implement either the Scala interface and forward the calls to the underlying Java collection, or … Read more
As a general rule, default to using Vector. It’s faster than List for almost everything and more memory-efficient for larger-than-trivial sized sequences. See this documentation of the relative performance of Vector compared to the other collections. There are some downsides to going with Vector. Specifically: Updates at the head are slower than List (though not … Read more
The answer is found on the definition of map: def map[B, That](f : (A) => B)(implicit bf : CanBuildFrom[Repr, B, That]) : That Note that it has two parameters. The first is your function and the second is an implicit. If you do not provide that implicit, Scala will choose the most specific one available. … Read more
I hope it’s not a “suicide note”, but I can see your point. You hit on what is at the same time both a strength and a problem of Scala: its extensibility. This lets us implement most major functionality in libraries. In some other languages, sequences with something like map or collect would be built … Read more