{"id":1090,"date":"2018-07-30T22:58:03","date_gmt":"2018-07-30T20:58:03","guid":{"rendered":"http:\/\/www.albertopasca.it\/whiletrue\/?p=1090"},"modified":"2018-07-29T20:05:40","modified_gmt":"2018-07-29T18:05:40","slug":"swift-chaining-methods","status":"publish","type":"post","link":"https:\/\/www.albertopasca.it\/whiletrue\/swift-chaining-methods\/","title":{"rendered":"Swift – Chaining methods"},"content":{"rendered":"

Very often in Swift, you can see various methods called one each other and linked by a dot “.”.<\/p>\n

These methods are called chained methods. Probably\u00a0using Alamofire you already have seen this behaviour:<\/p>\n

<\/p>\n

\n
Alamofire\r\n    .request<\/span><\/strong>(\"<\/span>https:\/\/httpbin.org\/basic-auth\/\\(<\/span>user<\/span>)<\/span><\/span>\/\\(<\/span>password<\/span>)<\/span><\/span>\"<\/span><\/span>)\r\n    .authenticate<\/span><\/strong>(user<\/span>: user, password<\/span>: password)\r\n    .responseJSON<\/span><\/strong> { response in<\/span>\r\n        debugPrint<\/span>(response)\r\n    }<\/pre>\n
In this piece of code,<\/p>\n
    \n
  • request<\/em><\/li>\n
  • authenticate<\/em><\/li>\n
  • responseJSON<\/em><\/li>\n<\/ul>\n
    are three different methods that return an Alamofire<\/em> object (self<\/strong>).<\/p>\n
    It’s very easy to do, but let’s see how it works and how we can do the same things!<\/p>\n<\/div>\n
    Let’s take a look at this basic class:<\/p>\n
    class<\/span> StringOperationsWithoutChain {\r\n\u00a0 \u00a0 <\/span>var<\/span> theString = \"\"<\/span>\r\n\u00a0 \u00a0 <\/span>init<\/span><\/strong>(str: String<\/span>) { theString<\/span> = str }\r\n\u00a0 \u00a0 <\/span>func<\/span> appendZero<\/strong>() -> String<\/span> { return<\/span> \"<\/span>\\(<\/span>theString<\/span>)0\"<\/span> }\r\n\u00a0 \u00a0 <\/span>func<\/span> appendOne<\/strong>()\u00a0 <\/span>-> String<\/span> { return<\/span> \"<\/span>\\(<\/span>theString<\/span>)1\"<\/span> }\r\n\u00a0 \u00a0 <\/span>func<\/span> appendIcs<\/strong>()\u00a0 <\/span>-> String<\/span> { return<\/span> \"<\/span>\\(<\/span>theString<\/span>)x\"<\/span> }\r\n}<\/pre>\n
    this class contains a simple init, and three (useless) methods.<\/p>\n
    You can use this class in this way:<\/p>\n
    let<\/span> str = <\/span>StringOperationsWithoutChain(str: <\/span>\"pippo\"<\/span>).<\/span>appendIcs<\/span><\/strong>()<\/span>\r\nprint( <\/span>str<\/span> )<\/span><\/pre>\n
    You create the class\u00a0StringOperationsWithoutChain(str: ” “)<\/strong> and next you call one of the methods inside.<\/p>\n
    You can do the same with:<\/p>\n
    let<\/span> str = <\/span>StringOperationsWithoutChain(str: <\/span>\"pippo\"<\/span>)<\/span>\r\nstr<\/span>.<\/span>appendIcs()<\/span>\r\nprint( <\/span>str<\/span> )<\/span><\/pre>\n
    You’re able to do this because str is of type\u00a0StringOperationsWithoutChain.<\/em><\/p>\n
    Let’s chain now:<\/h6>\n
    We can use the same class, refactored to be chainable. All the functions that we want to use in a chain must return the class itself<\/em>.<\/p>\n
    Example:<\/p>\n
    class<\/span> StringOperations {\r\n\u00a0 \u00a0 <\/span>var<\/span> theString = \"\"<\/span>\r\n\r\n\u00a0 \u00a0 <\/span>init<\/span>(str: String<\/span>) { \/\/ chainable, returns implicitly self\r\n\u00a0 \u00a0 \u00a0 \u00a0 <\/span>theString<\/span> = str\r\n\u00a0 \u00a0 <\/span>}\r\n\r\n\u00a0 \u00a0 <\/span>func<\/span> appendZero<\/strong>() -> StringOperations<\/span><\/strong> { \/\/ chainable\r\n\u00a0 \u00a0 \u00a0 \u00a0 <\/span>theString<\/span> += \"0\"<\/span>\r\n\u00a0 \u00a0 \u00a0 \u00a0 <\/span><\/span>return self\r\n\u00a0 \u00a0 <\/span>}\r\n\r\n\u00a0 \u00a0 <\/span>func<\/span> appendOne<\/strong>() -> StringOperations<\/span><\/strong> { \/\/ chainable\r\n\u00a0 \u00a0 \u00a0 \u00a0 <\/span>theString<\/span> += \"1\"<\/span>\r\n\u00a0 \u00a0 \u00a0 \u00a0 <\/span><\/span>return self\r\n\u00a0 \u00a0 <\/span>}\r\n\r\n\u00a0 \u00a0 <\/span>func<\/span> appendIcs<\/strong>() -> StringOperations<\/span><\/strong> {\/\/ chainable\r\n\u00a0 \u00a0 \u00a0 \u00a0 <\/span>theString<\/span> += \"x\"<\/span>\r\n\u00a0 \u00a0 \u00a0 \u00a0 <\/span><\/span>return self\r\n\u00a0 \u00a0 <\/span>}\r\n\r\n    \/\/ not chainable\r\n\u00a0 \u00a0 <\/span>func<\/span> printCallback<\/strong>(completion: @escaping<\/span> (_<\/span> result: String<\/span>) -> Void<\/span>) {\r\n\u00a0 \u00a0   \u00a0 <\/span>completion(theString<\/span>)\r\n\u00a0 \u00a0 <\/span>}\r\n}<\/pre>\n
    How to use this class?<\/p>\n
    \/\/ initialize\r\nStringOperations(str: <\/span>\"pippo\"<\/span>)<\/span><\/pre>\n
    and next we can chain all the methods you want:<\/p>\n
    StringOperations(str: <\/span>\"pippo\"<\/span>)<\/span>\r\n\u00a0 \u00a0 <\/span>.<\/span>appendOne()<\/span>\r\n\u00a0 \u00a0 <\/span>.<\/span>appendZero()<\/span>\r\n\u00a0 \u00a0 <\/span>.<\/span>appendIcs()<\/span>\r\n\u00a0 \u00a0 <\/span>.printCallback<\/span> { (result) in<\/span>\r\n\u00a0 \u00a0 \u00a0 \u00a0 <\/span>print<\/span>( result )\r\n}<\/pre>\n
    You create a string “pippo<\/strong>” and next add “1<\/strong>“, “0<\/strong>” and “X<\/strong>” to this string and print in a callback the result.<\/p>\n
    As you can confirm, is very simple and very useful!<\/p>\n
    Result in the console:<\/p>\n
    pippo10x<\/span><\/pre>\n
    Can be of course more interesting that appending values to a string. It’s just to make the idea and explain how it works.<\/p>\n
    Happy chain.<\/p>\n","protected":false},"excerpt":{"rendered":"
    Very often in Swift, you can see various methods called one each other and linked by a dot “.”. These methods are called chained methods. Probably\u00a0using Alamofire you already have seen this behaviour:<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[1],"tags":[687,686,682,683,684,685,222,46],"class_list":["post-1090","post","type-post","status-publish","format-standard","hentry","category-generic","tag-alamofire","tag-append","tag-chain","tag-chainable-methods","tag-closures","tag-completion","tag-string","tag-swift"],"yoast_head":"\nSwift - Chaining methods - while (true) {\u00a0}<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.albertopasca.it\/whiletrue\/swift-chaining-methods\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Swift - Chaining methods - while (true) {\u00a0}\" \/>\n<meta property=\"og:description\" content=\"Very often in Swift, you can see various methods called one each other and linked by a dot “.”. 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