I must say that the example copied out of the Scala documentation by skaffman above is of limited utility in practice (you might as well use case objects). In order to get something most closely resembling a Java Enum (i.e. with sensible toString and valueOf methods — perhaps you are persisting the enum values to … Read more
As so many others have said, the object assigned to a val cannot be replaced, and the object assigned to a var can. However, said object can have its internal state modified. For example: class A(n: Int) { var value = n } class B(n: Int) { val value = new A(n) } object Test … Read more
While all the previous responses are correct, they’re all in Java. Here’s a Scala example: val placeholder = “Hello %s, isn’t %s cool?” val formatted = placeholder.format(“Ivan”, “Scala”) I also have a blog post about making format like Python’s % operator that might be useful.
I’ll explain the main use cases of implicits below, but for more detail see the relevant chapter of Programming in Scala. Implicit parameters The final parameter list on a method can be marked implicit, which means the values will be taken from the context in which they are called. If there is no implicit value … Read more
I think the accepted answer is great, but it seems many people have failed to grasp some fundamental points. First, Scala’s for comprehensions are equivalent to Haskell’s do notation, and it is nothing more than a syntactic sugar for composition of multiple monadic operations. As this statement will most likely not help anyone who needs … Read more
Algebras I think the place to start would be to understand the idea of an algebra. This is just a generalization of algebraic structures like groups, rings, monoids and so on. Most of the time, these things are introduced in terms of sets, but since we’re among friends, I’ll talk about Haskell types instead. (I … Read more
val lines = scala.io.Source.fromFile(“file.txt”).mkString By the way, “scala.” isn’t really necessary, as it’s always in scope anyway, and you can, of course, import io’s contents, fully or partially, and avoid having to prepend “io.” too. The above leaves the file open, however. To avoid problems, you should close it like this: val source = scala.io.Source.fromFile(“file.txt”) … Read more
Mathematicians have their own little funny ways, so instead of saying “then we call function f passing it x as a parameter” as we programmers would say, they talk about “applying function f to its argument x“. In mathematics and computer science, Apply is a function that applies functions to arguments. Wikipedia apply serves the … Read more
In Java terms, Scala’s Seq would be Java’s List, and Scala’s List would be Java’s LinkedList. Note that Seq is a trait, which is equivalent to Java’s interface, but with the equivalent of up-and-coming defender methods. Scala’s List is an abstract class that is extended by Nil and ::, which are the concrete implementations of … Read more
I tried once to write about this, but I gave up in the end, as the rules are somewhat diffuse. Basically, you’ll have to get the hang of it. Perhaps it is best to concentrate on where curly braces and parenthesis can be used interchangeably: when passing parameters to method calls. You may replace parenthesis … Read more