Dictionary and Set Improvements in Swift 4.0

In the latest release of Swift, dictionaries and sets gain a number of new methods and initializers that make common tasks easier than ever. Operations like grouping, filtering, and transforming values can now be performed in a single step, letting you write more expressive and efficient code.

→ swift.org/blog/dictionary-and-set-improvements/

Swift 4 adds new methods and initialisers to dictionaries and sets that simplify tasks like grouping, filtering, and transforming data. For example, the Dictionary(grouping:by:) initialiser lets you group a sequence into a dictionary by a key, such as sorting groceries by department in one line of code.

Other features include mapValues(_:) to change values while keeping keys, merging dictionaries with custom handling for duplicate keys, and a default subscript for safe access or updates with a fallback value. Sets now return filtered results as sets, and both types offer capacity control and specialised collections for keys and values.

These changes improve code efficiency and readability, with most available in Swift 3.2 compatibility mode.