Static Library and Swift

Question

So I'm working on an iOS project in Swift, and I wanted to create a Static library with some useful stuff in it.

My problem is when I try to build my lib in Xcode (version 6.3) I have a "Build Failed" followed by : /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/libtool: unknown option character 'X' in: -Xlinker

I've never saw this and it's not my first static lib. So I was thinking I may be linked to the fact that I'm using exclusively Swift class.

What do you guys think ? Thank you in advance.

Eyespot

The accepted answer is no longer accurate. As of Xcode 9 beta 4 Swift can be used in static libraries, though some scenarios required extra configuration. See my answer below. – Agape

Answer 1

As of Xcode 9 beta 4, Xcode natively supports static libraries with Swift sources.

Masonite

What do I have to do to enable it? When using a static lib which contains swift, how do you access the headers from an objective-c project? – Toxicogenic

@HariKaramSingh I answered the OP question and yours in a separate answer. – Agape

For me, this problem started appearing again on Xcode 9.2 (9C40b), after a pod update. Probably a swift pod I'm using changed a setting. – Larimer

Answer 2

As mentioned, Apple does allow Swift in static libraries as of Xcode 9 Beta 4.

We attempted to do this on an existing project with an Objective-C-based target and "child" static library projects and kept running into a linking error

ld: library not found for -lswiftSwiftOnoneSupport for architecture x86_64

also

ld: library not found for -lswiftDispatch for architecture x86_64

This is because the main target (app) is trying to build solely against Objective-C and isn't told by the static library that it needs to include Swift libraries. This was because there weren't any Swift files in the Compile Sources section of our Build Phases for the app target.

So basically all you have to do is add at least one .swift file to that compile list and it will include the Swift libraries for you. It doesn't even need to have any code or values in it, it can be an empty file.

Then you can start adding Swift files to your "child" static library project. I would let it generate the bridging header for you at first then you can move it around and change what gets imported (make sure the project points to the right file in the build settings if you move it).

You should still keep in mind that using Swift and Objective-C within the same static library may have issues of its own. I suggest reading the Apple developer doc "Swift and Objective-C in the Same Project" on how to address importing Objective-C into Swift (using a bridging header) and how to use the Swift files in your Objective-C code (importing the generated -Swift.h for your library).

Agape

In my case, I was seeing ld: library not found for -lswiftCoreImage for architecture x86_64. This answer solved my linking issues. – Gt

@afarnham I think it will do so for pretty much every library in the Swift "core" since it's attempting to link with them when linking in the stuff from the static library that's using Swift. I previously attempted to manually include every Swift library with the target dependencies and other build phases; needless to say it was a nightmare...and didn't work. I would hope Apple would make this a project setting so you don't have to have a dummy file in place to "trick" the primary target but this works for now I guess. – Agape

Dean Kelly - I am able to create static lib contains swift classes. But how could I access swift class from static library to main app ? – Undesigning

@Vijay - That is a good candidate for separate question on SO. It depends on what type of file you are importing it into. Say for example your main app "FooApp" has a sub static library called "LibBar" and LibBar has a mix of Swift and ObjC. If you want to import a swift class from LibBar into an ObjC file in FooApp you have to import "LibBar/LibBar-Swift.h". If you want to use a LibBar Swift class in a Swift class in FooApp there are several ways: make LibBar publish a module with a modulemap and import that directly or import "LibBar/LibBar-Swift.h" in your FooApp bridging header. – Agape

@thibautnoah It's not a perfect integration by any means. You will have a tough time going from Swift to ObjC between two static libraries (that neither are the main app). It gets to the point it makes sense to create an adjacent static library for your Swift code that inherits from your ObjC one and then import both of those into the third library but that's to solve specific issues. – Agape

I just have a static library with a mix of objective-c and swift and i couldn't get the project (react-native) to compile :) – Vaasta

Amazing, just add a empty Swift file and all those errors go away. Thanks for the help! – Albinaalbinism

I envy @thibautnoah. I have had this issue for several weeks now! Thanks a million! – Lambertson

Same will go if you Swift Static library uses C/C++, then you need to create at least one C++ file in your client project before building the client app. Otherwise you get lot of random linker errors. – Maganmagana

Answer 3

Swift doesn't support static library

Although the correct way should be create a framework, there is a workaround here.

Keep

That is pretty annoying. Thank you for your answer. – Eyespot

Hi, since swift doesn't support static library, how can I prevent my colleagues from reading my code ? (It's about encrypting data, so the fewer people know about it, the better). My app also support ios 7, so I guess I cannot use framework, right ? – Generalization

might need update until now ? swift support both framework and static lib now ? – Preheat

From objective c project we can create static library but is it possible to create static library from Swift project as of xcode 8 – Camise

Is there any solution using static library in swift 3, I have a encryption library which has only two .a files on vendors sample (written in objective-c ) is working file, When i tried to use those library with using bridging header, (obviously bridging header configuration is fine as other objective-c libs are working fine on ) , it cannot is throwing error. Any one got solution regarding this issue then kindly post some clue. – Pythagoras

Swift support static library now. This answer is very old. – Murvyn

Answer 4

Swift consumer -> Swift static library

Xcode version 10.2.1

Create Swift static library

Create a library project or create a library target

File -> New -> Project... -> Cocoa Touch Static Library
//or
Project editor -> Add a Target -> Cocoa Touch Static Library 

Add files .swift

Select `.swift` file -> Select File Inspectors Tab -> Target Membership -> Select the target
//or
Project editor -> select a target -> Build Phases -> Compile Sources -> add files

Build library - ⌘ Command + B or Product -> Build

Note 1: Be sure that you build library for the same process architecture as the client code.
Note 2: expose your API that should be visible for consumer using public or open access modifiers^[About]

Find generated output^{[Build location]}

Products group -> lib<product_name>.a -> Show in Finder

The directory includes

• lib<product_name>.a – a built static library
• <product_name>.swiftmodule. swiftmodule describe an interface of a library and a compiler version. This folder includes:
• .swiftdoc - docs
• .swiftmodule - public interface/definitions

Swift consumer with Swift static library

Drag and drop the binary into the Xcode project^[About]

Link Binary^{[Undefined symbols] [Link vs Embed]}

Project editor -> select a target -> General -> Linked Frameworks and Libraries -> add -> Add Others... -> point to `lib<target_name>.a` file
//or
Project editor -> select a target -> Build Phases -> Link Binary With Libraries -> add -> Add Others... -> point to `lib<target_name>.a` file

Add Library Search paths(LIBRARY_SEARCH_PATHS)^{[Library not found for] [Recursive path]}

Project editor -> select a target -> Build Settings -> Search Paths -> Library Search paths -> add path to the parent of `lib<target_name>.a` file

Add Import Paths^{[No such module] [Recursive path]}

Project editor -> select a target -> Build Settings -> Swift Compiler - Search Paths -> Import Paths -> add path to a folder with `.swiftmodule`

Import module to the Swift client code ^{[module_name]}

import module_name

[More examples]

Musical

I've built the static framework in its own self-contained project. I see the .a file and the .swiftmodule folder. I should drag both of them into my host app and then try to find the paths. Right? – Babysit

Sorry to ask, but any notes on this? – Babysit

Hello @Honey, I will check it again and provide you an information – Musical

@Honey, answering for your question, after building a library you should do 3 steps: 1. Drag .a file into your host app under Linked Frameworks and Libraries section. 2. Specify a path to .a fine under the Library Search paths section 3. Specify a path to .swiftmodule fine under the Import Paths section. I have just checked the tutorial and updated a post. If you have some issue pleas feel free to ask – Musical

@yoAlex5, Thanks a lot for your detailed and comprehensive explanation. The only thing I'd like to add it's that you have not to forget to mark your classes and methods public to make them available in other targets. Without that, you will be able to import the library but you can't use its code. Also, pay your attention that inits must be made public explicitly. – Coo

what if the library need to reference a third party library? – Poe