As previously discussed, Kotlin collections fall under two categories: mutable and immutable, and sets are no exception. An immutable set is declared using the setOf keyword and indicates a set whose values cannot change throughout a program:

var/val setName = setOf(val1, val2, val3) 

Note: Similarly to lists, the set type can be inferred by the compiler or declared in the code. For example, a set comprised of String values would be inferred as a Set<String>.

In the code below, we are creating a new set and storing it in the variable, colorsOftheRainbow:

var colorsOfTheRainbow = setOf("red", "orange", "yellow", "green", "blue", "red")

Logging colorsOfTheRainbow to the console, notice that there is one less color in the set. The last element, "red", was a duplicate String that the set object recognized and removed:

println(colorsOfTheRainbow)

// Prints: [red, orange, yellow, green, blue] 

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