Set and MutableSet

Just like List, Set also has the following two variants in Kotlin:

• Set
• MutableSet

Set is read-only and MutableSet is the mutable version of Set, which contains the read-write functionalities.

Note

Just like with list, set values also have read-only functions and properties like size, iterator(), and so on. We are skipping mentioning them here to avoid redundant contents in this book. Also, please note that set doesn't do ordering like list (unless you use OrderedSet). So, it lacks the functions which involve orders like indexOf(item), add(index, item), and so on.

Sets in collections represent mathematical sets (as in set theory).

The following is an example with MutableSet:

fun main(args: Array<String>) { 
    val set = mutableSetOf(1,2,3,3,2) 
 
    println("set $set") 
 
    set.add(4) 
    set.add(5) 
    set.add(5) 
    set.add(6) 
 
    println("set $set") 
} 

The following is the output:

The output clearly shows that, even though we added multiple duplicate items to...