Set.insert() / remove() / contains()

// Declaring and initializing a Set
var set: Set<String> = ["apple", "banana", "cherry"]
var emptySet = Set<Int>()               // Empty Set
var set2: Set = ["a", "b", "c"]         // Type inference

// Checking if an element exists
set.contains("apple")                   // true

// Creating a Set
var fruits: Set<String> = ["apple", "banana", "cherry"]
print("Initial: \(fruits)")

// insert: Add an element (check result with the return value)
let (inserted, member) = fruits.insert("grape")
print("Insert grape: \(inserted ? "succeeded" : "already exists") - \(member)")

// Attempting to insert a duplicate
let (inserted2, _) = fruits.insert("apple")
print("Insert apple again: \(inserted2 ? "succeeded" : "already exists")")

// contains: Check if an element exists
print("banana exists: \(fruits.contains("banana"))")
print("mango exists: \(fruits.contains("mango"))")

// remove: Remove an element
if let removed = fruits.remove("banana") {
    print("Removed: \(removed)")
}
print("After removal: \(fruits)")

// count / isEmpty
print("Count: \(fruits.count)")
print("Empty: \(fruits.isEmpty)")

// Iterating with for-in (order is not guaranteed)
print("List:")
for fruit in fruits.sorted() {
    print("  \(fruit)")
}

A Set automatically eliminates duplicates. Even if an array contains duplicates, converting it with Set(array) removes them.

The return value of insert(_:) is a tuple of type (inserted: Bool, memberAfterInsert: Element). If the element already exists, the existing element is returned. Elements in a Set must conform to Hashable. If you use a custom type, you must add Hashable conformance.

For set operations between sets, see set.union() / intersection() / subtracting().