What are sets?

Written by Paul Hudson    @twostraws

Sets are a type of sequence similar to arrays, except they may not store any item more than once and are unordered. This eliminates them from many places where you would use an array, but they do have one special super-power: it’s extremely fast to check whether a set contains a specific value. In fact, sets perform this operation at the same speed whether they contain 10 items or 10,000 items.

Sets can be created directly from arrays, then used like them in many ways. For example:

var numbers = Set([1, 2, 3])

You can then go ahead and check whether that contains a specific value, like this:

print(numbers.contains(5))

Because sets don’t have any concept of ordering, they don’t have an append() method. Instead, they use insert(), like this:

numbers.insert(5)

Available from iOS – learn more in my book Pro Swift

Did this solution work for you? Please pass it on!

Tweet

Other people are reading…

• How to convert an int to a float
• What is an optional value in Swift?
• How to use typealias to make it easier to use complex types
• Optional vs implicitly unwrapped optional: what’s the difference?
• Private vs fileprivate: what’s the difference?

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.