{"id":1897,"date":"2019-05-19T07:59:17","date_gmt":"2019-05-19T07:59:17","guid":{"rendered":"http:\/\/demensdeum.com\/blog\/?p=1897"},"modified":"2024-12-16T22:32:38","modified_gmt":"2024-12-16T19:32:38","slug":"strategy-pattern","status":"publish","type":"post","link":"https:\/\/demensdeum.com\/blog\/pt\/2019\/05\/19\/strategy-pattern\/","title":{"rendered":"Strategy pattern"},"content":{"rendered":"

The Strategy pattern allows you to select the type of algorithm that implements a common interface, right while the application is running. This pattern refers to the behavioral design patterns.<\/p>\n

\"\"<\/a>
Sun Tzu<\/a><\/figcaption><\/figure>\n

Suppose we are developing a music player with embedded codecs. The built-in codecs imply reading music formats without using external sources of the operating system (codecs), the player should be able to read tracks of different formats and play them. VLC player has such capabilities, it supports various types of video and audio formats, it runs on popular and not very operating systems.<\/p>\n

Imagine what a naive player implementation looks like:<\/p>\n

<\/p>\n

\n
var<\/span> player: MusicPlayer?\r\n\r\nfunc play<\/span>(filePath: String) {\r\n    let extension = filePath.pathExtension\r\n\r\n    if<\/span> extension == \"mp3\"<\/span> {\r\n        playMp3(filePath)\r\n    }\r\n    else<\/span> if<\/span> extension == \"ogg\"<\/span> {\r\n        playOgg(filePath)\r\n    }\r\n}\r\n\r\nfunc playMp3<\/span>(_ filePath: String) {\r\n    player = MpegPlayer()\r\n    player?.playMp3(filePath)\r\n}\r\n\r\nfunc playOgg<\/span>(_ filePath: String) {\r\n    player = VorbisPlayer()\r\n    player?.playMusic(filePath)\r\n}\r\n<\/pre>\n<\/div>\n
Next, we add several formats, which leads to the need to write additional methods.<\/span> Plus, the player must support plug-in libraries, with new audio formats that will appear later.<\/span> There is a need to switch the music playback algorithm, the Strategy pattern is used to solve this problem.<\/span><\/span><\/p>\n
Let’s create a common protocol MusicPlayerCodecAlgorithm, write the implementation of the protocol in two classes MpegMusicPlayerCodecAlgorithm and VorbisMusicPlayerCodecAlgorithm, to play mp3 and ogg files with-but.<\/span> Create a class MusicPlayer, which will contain a reference for the algorithm that needs to be switched, then by the file extension we implement codec type switching:<\/span><\/span><\/p>\n
<\/p>\n
\n
import Foundation\r\n\r\nclass<\/span> MusicPlayer<\/span> {\r\n    var<\/span> playerCodecAlgorithm: MusicPlayerCodecAlgorithm?\r\n    \r\n\tfunc play<\/span>(_ filePath: String) {\r\n            playerCodecAlgorithm?.play(filePath)\r\n\t}\r\n}\r\n\r\nprotocol MusicPlayerCodecAlgorithm {\r\n    func play<\/span>(_ filePath: String)\r\n}\r\n\r\nclass<\/span> MpegMusicPlayerCodecAlgorithm<\/span>: MusicPlayerCodecAlgorithm {\r\n\tfunc play<\/span>(_ filePath: String) {\r\n\t\tdebugPrint(\"mpeg codec - play\"<\/span>)\r\n\t}\r\n}\r\n\r\nclass<\/span> VorbisMusicPlayerCodecAlgorithm<\/span>: MusicPlayerCodecAlgorithm {\r\n\tfunc play<\/span>(_ filePath: String) {\r\n\t\tdebugPrint(\"vorbis codec - play\"<\/span>)\t\r\n\t}\r\n}\r\n\r\nfunc play<\/span>(fileAtPath path: String) {\r\n\tguard let url = URL(string: path) else<\/span> { return<\/span> }\r\n\tlet fileExtension = url.pathExtension\r\n\t\t\r\n\tlet musicPlayer = MusicPlayer()\r\n\tvar<\/span> playerCodecAlgorithm: MusicPlayerCodecAlgorithm? \r\n\t\t\r\n\tif<\/span> fileExtension == \"mp3\"<\/span> {\r\n                playerCodecAlgorithm = MpegMusicPlayerCodecAlgorithm()\r\n\t}\r\n\telse<\/span> if<\/span> fileExtension == \"ogg\"<\/span> {\r\n                playerCodecAlgorithm = VorbisMusicPlayerCodecAlgorithm()\r\n\t}\r\n\t\t\r\n\tmusicPlayer.playerCodecAlgorithm = playerCodecAlgorithm\r\n\tmusicPlayer.playerCodecAlgorithm?.play(path)\r\n}\r\n\r\nplay(fileAtPath: \"Djentuggah.mp3\"<\/span>)\r\nplay(fileAtPath: \"Procrastinallica.ogg\"<\/span>)\r\n<\/pre>\n<\/div>\n
The above example also shows the simplest example of a factory (switching the codec type from the file extension) It is important to note that the Strategy strategy does not create objects, it only describes how to create a common interface for switching the family of algorithms.<\/span><\/span><\/p>\n
Documentation<\/h3>\n
https:\/\/refactoring.guru\/en\/design-patterns\/strategy<\/a><\/p>\n
Source code<\/h3>\n
https:\/\/gitlab.com\/demensdeum\/patterns\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"
The Strategy pattern allows you to select the type of algorithm that implements a common interface, right while the application is running. This pattern refers to the behavioral design patterns. Suppose we are developing a music player with embedded codecs. The built-in codecs imply reading music formats without using external sources of the operating systemContinue reading “Strategy pattern”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[61,52],"tags":[95,102],"class_list":["post-1897","post","type-post","status-publish","format-standard","hentry","category-techie","category-tutorials","tag-patterns","tag-strategy","entry"],"translation":{"provider":"WPGlobus","version":"3.0.2","language":"pt","enabled_languages":["en","ru","zh","de","fr","ja","pt"],"languages":{"en":{"title":true,"content":true,"excerpt":false},"ru":{"title":true,"content":true,"excerpt":false},"zh":{"title":false,"content":false,"excerpt":false},"de":{"title":false,"content":false,"excerpt":false},"fr":{"title":false,"content":false,"excerpt":false},"ja":{"title":false,"content":false,"excerpt":false},"pt":{"title":false,"content":false,"excerpt":false}}},"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/demensdeum.com\/blog\/pt\/wp-json\/wp\/v2\/posts\/1897","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/demensdeum.com\/blog\/pt\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/demensdeum.com\/blog\/pt\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/demensdeum.com\/blog\/pt\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/demensdeum.com\/blog\/pt\/wp-json\/wp\/v2\/comments?post=1897"}],"version-history":[{"count":23,"href":"https:\/\/demensdeum.com\/blog\/pt\/wp-json\/wp\/v2\/posts\/1897\/revisions"}],"predecessor-version":[{"id":1941,"href":"https:\/\/demensdeum.com\/blog\/pt\/wp-json\/wp\/v2\/posts\/1897\/revisions\/1941"}],"wp:attachment":[{"href":"https:\/\/demensdeum.com\/blog\/pt\/wp-json\/wp\/v2\/media?parent=1897"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/demensdeum.com\/blog\/pt\/wp-json\/wp\/v2\/categories?post=1897"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/demensdeum.com\/blog\/pt\/wp-json\/wp\/v2\/tags?post=1897"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}