CFBag

A bag, or multiset is a variant of a set, where members can appear more than once. A count is associated with each unique member of the collection, representing the number of times it has been added. Like with sets, order does not matter.

→ nshipster.com/cfbag/

The article explores the CFBag and CFMutableBag Core Foundation types, which implement a bag (multi-set) data structure, allowing multiple occurrences of elements with associated counts. Unlike the toll-free bridged NSArray/CFArray, NSDictionary/CFDictionary, and NSSet/CFSet, but not NSCountedSet/CFBag due to the latter’s lack of a mutable counterpart.

CFBag offers customisable behaviour via CFBagCallBacks, enabling developers to define how values are retained, released, described, compared, and hashed, useful for applications like vote tallying or probability simulations.

It highlights the flexibility of CFMutableBag with functions like CFBagApplyFunction for transforming values, positioning it as a niche but powerful tool.

The article underscores the unique aspects of Objective-C’s blend of Smalltalk and C, reflected in Foundation and Core Foundation’s relationship, and teases other lesser-known types like CFBinaryHeap and NSMapTable for future exploration. Written in Swift, it encourages discovering hidden gems in Apple’s frameworks for innovative development.