scalatutorials

Collections · 31 of 42

Immutable collections with var

One thing to note is the difference between the +=, ++=, -=, --= etc. functions regarding mutable and immutable collections.

  • For immutable collections - they are not methods of the collection (since it’s not modifiable) but if used on an immutable collection declared with var instead of val then the Scala compiler expands them to variable = variable op param (see on the left for an example)
  • For mutable collections - they are actually methods on the collection, and they modify the collection when used.
import scala.collection.mutable

var immutableSet = Set(1, 2, 3)

immutableSet += 4
//this is the same as:
immutableSet = immutableSet + 4

//compare to
val mutableSet = mutable.Set(1, 2, 3)

mutableSet += 4
// this is the same as:
mutableSet.+=(4)

println(immutableSet)
println(mutableSet)

Contents

Scala basics

  1. Overview
  2. Scalculator
  3. Operators are methods
  4. Variables
  5. Final variables
  6. Printing values
  7. String interpolation
  8. String formatting
  9. Useful operations
  10. Method definition
  11. Method definition 2
  12. Method definition 3
  13. Anonymous functions
  14. Anonymous functions 2
  15. Return multiple values
  16. Declare multiple variables
  17. Assign multiple variables
  18. Loops using while
  19. Loops using for
  20. Loops without loops
  21. If
  22. Match as a switch
  23. Arrays
  24. Lists
  25. Sets
  26. Maps
  27. Mutable collections
  28. Collections: accessing elements
  29. Collections: concatenation
  30. Mutable collection operations
  31. Immutable collections with var
  32. Collections: useful methods
  33. Classes
  34. Classes, continued

What's new in Scala 3

  1. Scala 3: what changed
  2. Optional braces & new control syntax
  3. Top-level definitions & @main
  4. Enums & ADTs
  5. Extension methods
  6. given & using
  7. Union & intersection types
  8. Smaller niceties