Swift wants to let you write generic, reusable code<\/strong> that works with many different kinds of collections<\/strong> \u2014 not just Array.<\/p>\n Examples of different kinds of collections:<\/p>\n Instead of writing separate functions for each type:<\/p>\n Swift lets you write one generic function<\/strong> that works with all<\/strong> of them \u2014 as long as they conform to the right protocol.<\/p>\n That is the whole reason for Collection protocols.<\/p>\n Here is the most important family tree you should keep in mind:<\/p>\n You will mostly interact with these four:<\/p>\n Rule of thumb used by most good Swift developers:<\/strong><\/p>\n Real-life use-case \u2013 generic logging function<\/strong><\/p>\n This function works with Array<\/strong>, Set<\/strong>, Dictionary.keys<\/strong>, String<\/strong>, ArraySlice<\/strong>, etc.<\/p>\n Real-life example \u2013 safe slicing \/ pagination<\/strong><\/p>\n Array<\/strong>, ArraySlice, ContiguousArray conform to RandomAccessCollection. Set and Dictionary do not<\/strong> \u2014 their access is fast but not guaranteed O(1)<\/strong> for indexed access.<\/p>\n This one function works with Array, Set, Dictionary.keys, String, etc.<\/p>\n Rule of thumb used by most good Swift developers:<\/strong><\/p>\n Paste your code here if you want feedback or want to see cleaner versions!<\/p>\n What would you like to explore next?<\/p>\n Just tell me \u2014 we\u2019ll continue in the same clear, patient, detailed style \ud83d\ude0a<\/p>\n","protected":false},"excerpt":{"rendered":" 1. Why does Swift have Collection Protocols? (the most important big picture) Swift wants to let you write generic, reusable code that works with many different kinds of collections \u2014 not just Array. Examples...<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[76],"tags":[],"class_list":["post-2726","post","type-post","status-publish","format-standard","hentry","category-swift"],"_links":{"self":[{"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/posts\/2726","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/comments?post=2726"}],"version-history":[{"count":1,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/posts\/2726\/revisions"}],"predecessor-version":[{"id":2727,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/posts\/2726\/revisions\/2727"}],"wp:attachment":[{"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/media?parent=2726"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/categories?post=2726"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/tags?post=2726"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}\n
func printAll(array: [String]) { \u2026 }\r\nfunc printAll(set: Set<String>) { \u2026 }\r\nfunc printAll(dictKeys: Dictionary<String, Int>.Keys) { \u2026 }<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n2. The Main Collection Protocols \u2013 Hierarchy Overview<\/h3>\n
Sequence\r\n \u2191\r\nCollection \u2190 most important for everyday work\r\n \u2191\r\nBidirectionalCollection\r\n \u2191\r\nRandomAccessCollection \u2190 Array, ArraySlice, ContiguousArray belong here<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n\n\n
\n \nProtocol<\/th>\n Ordered?<\/th>\n Index type<\/th>\n Random access?<\/th>\n Typical types that conform<\/th>\n When you care about it<\/th>\n<\/tr>\n<\/thead>\n \n Sequence<\/strong><\/td>\n Yes<\/td>\n \u2014 (no index)<\/td>\n No<\/td>\n Array, Set, Dictionary, String, Range, StrideThrough\u2026<\/td>\n When you just iterate (for-in, forEach, map, filter\u2026)<\/td>\n<\/tr>\n \n Collection<\/strong><\/td>\n Yes<\/td>\n Index (opaque)<\/td>\n No (but fast in practice for Array)<\/td>\n Array, Set, Dictionary, String, ArraySlice\u2026<\/td>\n When you need .count, .isEmpty, subscript [index], .first, .last\u2026<\/td>\n<\/tr>\n \n BidirectionalCollection<\/strong><\/td>\n Yes<\/td>\n Supports going backward<\/td>\n No<\/td>\n Array, Set, Dictionary, String\u2026<\/td>\n When you need .last, .reversed(), iterate backward<\/td>\n<\/tr>\n \n RandomAccessCollection<\/strong><\/td>\n Yes<\/td>\n Supports fast jumping<\/td>\n Yes<\/td>\n Array, ArraySlice, ContiguousArray, Range\u2026<\/td>\n When you need fast random access coll[i] or slicing<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \n
3. Sequence \u2013 the foundation (what almost everything conforms to)<\/h3>\n
func printAllElements<S: Sequence>(_ items: S) where S.Element == String {\r\n for item in items {\r\n print(item)\r\n }\r\n}\r\n\r\nlet names = [\"Rahul\", \"Priya\", \"Aarav\"]\r\nlet uniqueNames = Set(names)\r\nlet nameString = \"RahulPriyaAarav\"\r\n\r\nprintAllElements(names) \/\/ Array\r\nprintAllElements(uniqueNames) \/\/ Set\r\nprintAllElements(nameString) \/\/ String<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nfunc logItems<S: Sequence>(_ items: S, prefix: String = \"\u2192\") where S.Element: CustomStringConvertible {\r\n items.forEach { item in\r\n print(\"\\(prefix) \\(item)\")\r\n }\r\n}\r\n\r\nlogItems([1, 2, 3]) \/\/ \u2192 1 \u2192 2 \u2192 3\r\nlogItems(Set([\"apple\", \"banana\"])) \/\/ \u2192 apple \u2192 banana (order not guaranteed)\r\nlogItems(\"hello\".map { $0 }) \/\/ \u2192 h \u2192 e \u2192 l \u2192 l \u2192 o<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n4. Collection \u2013 when you need count, indices, subscript<\/h3>\n
func printWithIndices<C: Collection>(_ items: C) where C.Element: CustomStringConvertible {\r\n if items.isEmpty {\r\n print(\"Empty collection\")\r\n return\r\n }\r\n \r\n print(\"Collection with \\(items.count) items:\")\r\n \r\n for (offset, element) in items.enumerated() {\r\n print(\" [\\(offset)] \\(element)\")\r\n }\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nfunc getPage<C: Collection>(_ items: C, page: Int, pageSize: Int = 10) -> C.SubSequence\r\n where C.Index == Int {\r\n \r\n let start = page * pageSize\r\n let end = min(start + pageSize, items.count)\r\n \r\n guard start < items.count else {\r\n return items[items.endIndex..<items.endIndex] \/\/ empty slice\r\n }\r\n \r\n return items[start..<end]\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n5. RandomAccessCollection \u2013 when you need fast random access<\/h3>\n
func swapFirstAndLast<C: RandomAccessCollection & MutableCollection>(_ collection: inout C) {\r\n guard !collection.isEmpty else { return }\r\n \r\n \/\/ Because it's RandomAccessCollection, subscript is O(1)\r\n let firstIndex = collection.startIndex\r\n let lastIndex = collection.index(before: collection.endIndex)\r\n \r\n collection.swapAt(firstIndex, lastIndex)\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nvar numbers = [10, 20, 30, 40, 50]\r\nswapFirstAndLast(&numbers)\r\nprint(numbers) \/\/ [50, 20, 30, 40, 10]<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n6. Real-life examples you will actually write<\/h3>\n
Example 1 \u2013 Generic function that works on any Collection<\/h4>\n
func printSummary<C: Collection>(_ items: C) where C.Element: CustomStringConvertible {\r\n if items.isEmpty {\r\n print(\"No items\")\r\n return\r\n }\r\n \r\n print(\"Showing \\(items.count) items:\")\r\n \r\n \/\/ Safe because Collection guarantees .first \/ .last\r\n if let first = items.first, let last = items.last {\r\n print(\" First: \\(first)\")\r\n print(\" Last: \\(last)\")\r\n }\r\n \r\n \/\/ enumerated() works because Collection has indices\r\n items.enumerated().forEach { index, item in\r\n print(\" #\\(index + 1): \\(item)\")\r\n }\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\nExample 2 \u2013 Safe pagination \/ slicing<\/h4>\n
func getPage<C: Collection>(_ items: C, page: Int, pageSize: Int = 20) -> C.SubSequence\r\n where C.Index == Int {\r\n \r\n let start = page * pageSize\r\n guard start < items.count else {\r\n return items[items.endIndex..<items.endIndex] \/\/ empty\r\n }\r\n \r\n let end = min(start + pageSize, items.count)\r\n return items[start..<end]\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n7. Quick Summary \u2013 Which protocol should you usually ask for?<\/h3>\n
\n\n
\n \nYou need\u2026<\/th>\n Minimum protocol you should ask for<\/th>\n Why? \/ Typical generic signature<\/th>\n<\/tr>\n<\/thead>\n \n Just iterate (for-in, forEach, map, filter)<\/td>\n Sequence<\/td>\n func process<S: Sequence>(_ items: S) where S.Element == String<\/td>\n<\/tr>\n \n Need .count, .isEmpty, .first, .last, subscript<\/td>\n Collection<\/td>\n func summary<C: Collection>(_ items: C)<\/td>\n<\/tr>\n \n Need fast random access \/ slicing<\/td>\n RandomAccessCollection<\/td>\n func swapFirstLast<C: RandomAccessCollection & MutableCollection>(_ c: inout C)<\/td>\n<\/tr>\n \n Need bidirectional walking (rare)<\/td>\n BidirectionalCollection<\/td>\n reversed(), backward iteration<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \n
8. Small Practice \u2013 Try these<\/h3>\n
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