{"id":7012,"date":"2014-06-26T13:30:08","date_gmt":"2014-06-26T10:30:08","guid":{"rendered":"http:\/\/railsware.com\/blog\/?p=7012"},"modified":"2021-08-11T18:38:32","modified_gmt":"2021-08-11T15:38:32","slug":"creation-of-pure-swift-module","status":"publish","type":"post","link":"https:\/\/railsware.com\/blog\/creation-of-pure-swift-module\/","title":{"rendered":"Creation of pure Swift module"},"content":{"rendered":"\n

If you have already started playing with swift, you probably thought about how to include third party libraries into your project or how to distribute yours.<\/p>\n\n\n\n

Apple provides a mechanism to distribute code via frameworks (eventually, for iOS too), so making a custom framework, which will include both ObjC and Swift code is very easy. But let’s dig deeper and create a pure<\/strong> Swift module, like apple does with Swift’ std lib and Cocoa\/CocoaTouch bridge.<\/p>\n\n\n\n

Note:<\/strong> this module will work in swift-only projects, in case if ObjC compiler generates Swift-to-ObjC bridging header and includes swift-module via @import<\/code> directive, which doesn’t work with current Xcode\/Apple Clang version.<\/em><\/p>\n\n\n\n

Toy Swift Module<\/h3>\n\n\n\n

We’re going to create a simple module call Logger<\/code> which will contain only one method: log<\/code>.<\/p>\n\n\n\n

You can see sample project here<\/a>.<\/p>\n\n\n\n

Each swift module consists of at least three files, so we should get all of them as an output:<\/p>\n\n\n\n

Logger.swiftmodule<\/code> – public interface\/definitions<\/p>\n\n\n\n

Logger.swiftdoc<\/code> – docs (surprisingly)<\/p>\n\n\n\n

libLogger.a<\/code> – built library (there also might be a dylib<\/code>, it depends on your task)<\/p>\n\n\n\n

Note:<\/strong> you should switch xcrun<\/code> to beta xcode’ version before running swift<\/code> commands<\/em><\/p>\n\n\n\n

sudo xcode-select -switch $xcode_dir\/Contents\/Developer<\/pre>\n\n\n\n
libLogger.a<\/h3>\n\n\n\n
Let’s create the simplest and useless Logger<\/code> “library”.<\/p>\n\n\n\n
class Logger\n{\n    var prefix: String\n    \n    init(_ prefix: String) \n    {\n        self.prefix = prefix\n    }\n    \n    func log<T>(object: T)\n    {\n        print(prefix)\n        println(object)\n    }\n}<\/pre>\n\n\n\n
The class just takes some prefix and logs it before actual object<\/p>\n\n\n\n
var logger = Logger(\"> \")\nlogger.log(\"Hello, World!\")<\/pre>\n\n\n\n
Now it’s time to make a libLogger.a<\/code>:<\/p>\n\n\n\n
xcrun swift -emit-library -emit-object Logger.swift -sdk $(xcrun --show-sdk-path --sdk macosx) -module-name Logger\nar rcs libLogger.a Logger.o<\/pre>\n\n\n\n
-emit-library<\/code> generates dynamically linked shared library, while -emit-object<\/code> generates object file and includes main<\/code> function<\/strong>, so you will have linker errors due to duplicated symbols.<\/p>\n\n\n\n
Solution is pretty simple: include both flags -emit-object<\/code> and -emit-library<\/code>, as I did above.<\/p>\n\n\n\n
Logger.swiftmodule<\/h3>\n\n\n\n
xcrun swift -emit-module Logger.swift -sdk $(xcrun --show-sdk-path --sdk macosx) -module-name Logger<\/pre>\n\n\n\n
This command will generate Logger.swiftdoc<\/code> and Logger.swiftmodule<\/code>.<\/p>\n\n\n\n
Now we have complete module and can integrate it into real project. Just create simple swift-project and add the files:<\/p>\n\n\n\n
\"swift_module_integration\"<\/a><\/figure>\n\n\n\n
Then setup ‘Import paths’ for Swift<\/p>\n\n\n\n
\"swift_import_paths\"<\/a><\/figure>\n\n\n\n
We’re ready to check how it works:<\/p>\n\n\n\n
import Foundation\nimport Logger\n\nvar logger = Logger(\"> \")\nlogger.log(\"Hello\")<\/pre>\n\n\n\n
Just run and you’ll see an expected output:<\/p>\n\n\n\n
> Hello<\/pre>\n\n\n\n
If you see linker errors, check your ‘Library search paths’ and ‘Other linker flags’ — they should contain path to libLogger.a<\/code> and -lLogger<\/code> respectively.<\/p>\n\n\n\n
Logger.swiftdoc<\/h3>\n\n\n\n
Let’s figure out how to deal with documentation.<\/p>\n\n\n\n
To add documentation to module you just need to comment it using \/\/\/<\/code>, e.g.:<\/p>\n\n\n\n
\/\/\/ Simple Logger\n\/\/\/\n\/\/\/ Constructor takes prefix string which will be printed before actual object\n\/\/\/\nclass Logger\n{\n    var prefix: String\n    \n    init(_ prefix: String)\n    {\n        self.prefix = prefix\n    }\n    \n    \/\/\/ Prints `object` with specified `prefix`\n    func log<T>(object: T)\n    {\n        print(prefix)\n        println(object)\n    }\n}<\/pre>\n\n\n\n
After integrating module into a project you will see documentation on the right<\/p>\n\n\n\n
\"Swift<\/a><\/figure>\n\n\n\n
But I didn’t manage to get it work without restarting Xcode after integrating.<\/p>\n\n\n\n
Conclusion<\/h3>\n\n\n\n
This approach is not very nice for “everyday” usage for a regular iOS\/OSX developer (because it requires creating and supporting Make\/CMake file), but it might be useful if you want to create pure module which doesn’t use ObjC at all.<\/p>\n\n\n\n
Also, Swift modules are similar to Java’s jar<\/code> binaries.<\/p>\n\n\n\n
The source code:<\/p>\n\n\n\n
import Foundation\n\n\/\/\/ Simple Logger\n\/\/\/\n\/\/\/ Constructor takes prefix string which will be printed before actual object\n\/\/\/\nclass Logger\n{\n    var prefix: String\n    \n    init(_ prefix: String)\n    {\n        self.prefix = prefix\n    }\n    \n    \/\/\/ Prints `object` with prefix\n    func log<T>(object: T)\n    {\n        print(prefix)\n        println(object)\n    }\n}<\/pre>\n\n\n\n
transforms into module interface without details of implementation<\/p>\n\n\n\n
\/\/\/ Simple Logger\n\/\/\/\n\/\/\/ Constructor takes prefix string which will be printed before actual object\n\/\/\/\nclass Logger {\n    var prefix: String\n    init(_ prefix: String)\n\n    \/\/\/ Prints `object` with prefix\n    func log<T>(object: T)\n}<\/pre>\n\n\n\n
So you can even distribute proprietary libraries without any problems (except of crazy reverse engineers), but I hope you won’t do this in favor of Open Source Software ;)<\/p>\n","protected":false},"excerpt":{"rendered":"
If you have already started playing with swift, you probably thought about how to include third party libraries into your project or how to distribute yours. Apple provides a mechanism to distribute code via frameworks (eventually, for iOS too), so making a custom framework, which will include both ObjC and Swift code is very easy….<\/p>\n","protected":false},"author":55,"featured_media":9449,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[3],"tags":[],"coauthors":["AlexDenisov"],"class_list":["post-7012","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-development"],"acf":[],"aioseo_notices":[],"categories_data":[{"name":"Engineering","link":"https:\/\/railsware.com\/blog?category=development"}],"post_thumbnails":"https:\/\/railsware.com\/blog\/wp-content\/uploads\/2014\/06\/swift_module_integration.png","amp_enabled":true,"_links":{"self":[{"href":"https:\/\/railsware.com\/blog\/wp-json\/wp\/v2\/posts\/7012","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/railsware.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/railsware.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/railsware.com\/blog\/wp-json\/wp\/v2\/users\/55"}],"replies":[{"embeddable":true,"href":"https:\/\/railsware.com\/blog\/wp-json\/wp\/v2\/comments?post=7012"}],"version-history":[{"count":20,"href":"https:\/\/railsware.com\/blog\/wp-json\/wp\/v2\/posts\/7012\/revisions"}],"predecessor-version":[{"id":13936,"href":"https:\/\/railsware.com\/blog\/wp-json\/wp\/v2\/posts\/7012\/revisions\/13936"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/railsware.com\/blog\/wp-json\/wp\/v2\/media\/9449"}],"wp:attachment":[{"href":"https:\/\/railsware.com\/blog\/wp-json\/wp\/v2\/media?parent=7012"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/railsware.com\/blog\/wp-json\/wp\/v2\/categories?post=7012"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/railsware.com\/blog\/wp-json\/wp\/v2\/tags?post=7012"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/railsware.com\/blog\/wp-json\/wp\/v2\/coauthors?post=7012"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}