Scala defines the contains method on all its collection classes.
Sets
Let’s say you have a set containing the nicknames of the guys in the band Rush, and you want to see whether a certain person is in the band. Just use contains:
1 2 3 4 5 6 | val rush = Set("Dirk", "Lerxst", "Pratt")val gotAlex = rush contains "Lerxst"// gotAlex: Boolean = trueval gotAngus = rush contains "Angus"// gotAngus: Boolean = false |
Arrays, Lists, and Vectors (Oh, My!)
Seq and the sequence-like classes all define the contains method:
1 2 3 4 5 6 7 8 9 10 11 12 13 | val rushSeq = Seq("Dirk", "Lerxst", "Pratt")val rushA = Array("Dirk", "Lerxst", "Pratt")val rushL = List("Dirk", "Lerxst", "Pratt")val rushV = Vector("Dirk", "Lerxst", "Pratt")val gotGene = rushSeq contains "Gene"// gotGene: Boolean = falseval gotNeil = rushA contains "Pratt"// gotNeil : Boolean = trueval gotAlex = rushL contains "Lerxst"// gotAlex : Boolean = trueval gotPeter = rushV contains "Peter"// gotPeter : Boolean = false |
Sequences and the like also define a containsSlice method that takes a sequence and checks it is found in the collection. Order does matter, though:
1 2 3 4 5 6 | val gotGedAndAl = rushSeq containsSlice Seq("Dirk", "Lerxst")// gotGedAndAl: Boolean = true// rushSeq has "Dirk" before "Lerxst", so the following failsval gotAlAndGed = rushSeq containsSlice Seq("Lerxst", "Dirk")// gotAlAndGed: Boolean = false |
Strings
Because Scala just uses Java’s String class, we inherit the following from Java:
1 2 3 4 | val gotX = "Lerxst" contains 'x'// gotX : Boolean = trueval gotA = "Lerxst" contains 'A'// gotA : Boolean = false |
Java overloads contains to accept a String as well as a char:
1 2 3 4 | val gotXs = "Lerxst" contains "xs"// gotXs : Boolean = trueval gotAb = "Lerxst" contains "Ab"// gotAb : Boolean = false |
Because a String is also a sequence, Scala extends String with containsSlice if you prefer (perhaps for idiomatic reasons) to use it instead of contains. It can take a String or a sequence of Chars:
1 2 3 4 | val gotXs = "Lerxst" containsSlice "xs"// gotXs : Boolean = trueval gotXs = "Lerxst" containsSlice Seq('x', 's')// gotXs : Boolean = true |
Maps
Map has a contains method, and it operates on the Map‘s keys, not its values or its key-value pairs:
1 2 3 4 5 6 | val rushM = Map( "Dirk" -> "bass", "Lerxst" -> "guitar", "Pratt" -> "drums")val gotGed = rushM contains "Dirk"// val gotGed : bool = true |
To look among a Map‘s values, get the valuesIterator first. I’m not wild about this interface. It should have been values instead, but values returns an Iterable, which has no contains method:
1 2 3 4 | val gotDrummer = rushM.valuesIterator contains "drums"// gotDrummer: Boolean = trueval gotSitarist = rushM.valuesIterator contains "sitar"// gotSitarist: Boolean = false |
There is no contains variant that searches on a key-value pair. You can define an extension method containsPair:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | object MapExt { implicit class RichMap[A,B](val m: Map[A,B]) extends AnyVal { def containsPair(p: (A,B)): Boolean = m get p._1 contains p._2 }}import MapExt._val gotGedOnBass = rushM containsPair ("Dirk" -> "bass")// gotGedOnBass: Boolean = trueval gotGedOnFlute = rushM containsPair ("Dirk" -> "flute")// gotGedOnFlute: Boolean = falseval gotGeorgeOnSitar = rushM containsPair ("George" -> "sitar")// gotGeorgeOnSitar: Boolean = false |