What are KeyValuePairs?
Swift version: 5.4
KeyValuePairs, somewhat confusingly known as DictionaryLiteral before Swift 5.0, is a useful data type that provides dictionary-like functionality with a handful of benefits:
- Your keys don’t need to conform to
Hashable. - You can add items with duplicate keys.
- The order in which you add items is preserved.
However, because KeyValuePairs doesn’t require its keys to be hashable, you don’t get the fast key look up of a regular dictionary – it’s O(n) rather than O(1) if you like Big O notation. Instead, you access them like an array, using numerical indexes.
As an example, here’s a KeyValuePairs instance holding the name of a singer:
let singer: KeyValuePairs = ["firstName": "Taylor", "lastName": "Swift"]If we wanted to access the key name and value for the first item, we’d write something like this:
print("\(singer[0].key) is set to \(singer[0].value)")Even better, because KeyValuePairs inherits from the Sequence protocol we can loop over all keys and values, like this:
for value in singer {
print("\(value.key) is set to \(value.value)")
}
SPONSORED Join a FREE crash course for iOS devs who want to become complete senior developers — from October 18th to 24th. Learn how to apply iOS app architecture patterns through a series of lectures and practical coding sessions.
Sponsor Hacking with Swift and reach the world's largest Swift community!
Available from iOS 8.0
Similar solutions…
- What's the difference between let and var?
- How to fix “argument of #selector refers to instance method that is not exposed to Objective-C”
- How to pass the Fizz Buzz test
- How to make optional protocol methods
- What’s the difference between init?() and init()?
About the Swift Knowledge Base
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.
