Hands-On Design Patterns with Swift

Iterating, mapping, and reducing

Dictionaries are collections; literally, Dictionary conforms to the collection type. Therefore, it gains lots of the features of collections.

The element type of the [Key: Value] collection is a (Key, Value) tuple.

Let's take a look at the different syntax, as follows:

for (key, value) in swiftReleases {    print("\(key) -> \(value)")}// Output:2016-09-13 -> Swift 3.02015-09-21 -> Swift 2.02017-09-19 -> Swift 4.02015-04-08 -> Swift 1.22014-09-09 -> Swift 1.02014-10-22 -> Swift 1.12018-03-29 -> Swift 4.1

As you can see, the order of keys is not preserved; this may affect your programs, if you expect the order to be consistent across runs. 

• Using forEach: This is very similar to using the for in pattern:

swiftReleases ...