kotlin-stdlib/kotlin.collections/AbstractMutableSet/add

add

actual abstract override fun add(element: E): Boolean(source)

Adds the specified element to the set.

This method is redeclared as abstract, because it's not implemented in the base class, so it must be always overridden in the concrete mutable collection implementation.

Since Kotlin

1.1

Return

true if the element has been added, false if the element is already contained in the set.