I saw some Scala code written as:
def next(): Array[String] = someVariable.next() :+ iterator.key Where someVariable has a method next() to get the next line and the iterator is of type Iterator[String].
What does :+ mean here?
- 3Is there some reason why you didn't just look this up in the scala doc? scala-lang.org/api/2.11.8/… The API documentation is fairly comprehensive, and my "go to" place for questions like this.The Archetypal Paul– The Archetypal Paul2016-05-12 15:23:00 +00:00Commented May 12, 2016 at 15:23
- It's cool new docs (2.12) give you this nice search feature scala-lang.org/files/archive/api/2.12.0-M4/index.html?search=:+mfirry– mfirry2016-05-12 20:12:43 +00:00Commented May 12, 2016 at 20:12
- @TheArchetypalPaul the time you took to write this stuff, could have answered him in a better way...AZ_– AZ_2018-05-16 20:12:53 +00:00Commented May 16, 2018 at 20:12
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3 Answers
On Scala Collections there is usually :+ and +:.
Both add an element to the collection. :+ appends +: prepends.
A good reminder is, : is where the Collection goes.
There is as well colA ++: colB to concat collections, where the : side collection determines the resulting type. If a :++ exists, it is the same as ++. In both cases the left side collection determines the type of result.
1 Comment
f4x
What is difference between
++ and :++?:+ is a method on whatever type is returned by someVariable.next().
Presumably it's scala.Array.:+
A copy of this array with an element appended.
This is also a case where an IDE would help you greatly. With Intellij for example, you could use the "Quick doc" or "Jump to definition" commands on :+ and immediately find out where it came from. I've found that tooling to be invaluable in writing scala.
Comments
scala> List(1,2,3,4) :+ 400 res27: List[Int] = List(1, 2, 3, 4, 400) 
2 Comments
4b0
While this code may solve the question, including an explanation really helps to improve the quality of your post.
jwvh
And with questions this old it can be quite helpful to explain how your answer is different from the existing answers.