Introduction

When working with Xcode 8, Swift 3, and CocoaPods, many developers encounter the `ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES` setting. Understanding this build setting is essential when dealing with Swift projects, especially those that integrate Objective-C, use dynamic frameworks, or share components across different projects. This setting ensures that the Swift Standard Libraries are correctly included in the final build, which can be crucial for preventing runtime crashes due to missing libraries.

Understanding `ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES`

What is it?

The `ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES` setting in Xcode dictates whether the Swift Standard Libraries are embedded in the app's bundle or not. Swift, unlike Objective-C, requires its standard libraries to be packaged with the application because they aren't part of the system libraries on all platforms yet. This setting, therefore, ensures that apps built with Swift have all the required dependencies packaged.

Default Values

• For Xcode projects that are primarily Swift, this setting is usually ON, particularly in apps that are not standalone iOS/macOS/watchOS apps.
• For a dynamic framework or when building an executable outside of App Store deployment bundles, you might want this set to OFF and have the necessary libraries linked appropriately.

Library Embedding Behavior

When set to YES:

• The build process embeds the Swift standard libraries as part of the app bundle. This ensures that any Swift-specific functionality will have the necessary runtime support, preventing potential issues after deployment.

When set to NO:

• This assumes that the environment where the app will run already includes the Swift Standard Libraries, or they will be provided by another means, such as another app on the system.

How `ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES` Works with CocoaPods

Using CocoaPods for dependency management in Swift apps can introduce another layer of complexity:

• CocoaPods has its own way of handling Swift libraries. When generating frameworks from pods, CocoaPods configures project settings with a consideration for Swift dependencies.
• If a CocoaPod is built with Swift, the resulting CocoaPods project might automatically modify this setting for easier integration.

To override or explicitly configure this in your project:

1. Open your Xcode project settings.
2. Navigate to the Build Settings tab.
3. Locate ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES.
4. Set this to YES for targets that need the Swift libraries embedded, or NO where they are not required.

Technical Explanation

This setting is vital for targets that use Swift frameworks. If your main app target is entirely in Swift or integrates many Swift-based Cocoapods, ensure this setting is correctly managed:

• Swift-only projects: Set this to YES if using CocoaPods for external dependencies, ensuring all Swift-based libraries are included.
• Mixed-language projects (Objective-C and Swift): Carefully configure each target. Objective-C targets using Swift dependencies need to enable this setting to avoid linker errors or runtime issues.

Example Configuration

• Ensure `ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES = YES` is set for `MyApp` to enable Swift standard library embedding.
• Deployment Target: Xcode 8 and Swift 3 require careful management of the deployment target to ensure that all necessary runtime components are present on devices with potentially older systems.
• Bitcode: If Bitcode is enabled in your project, ensure that the Swift Standard Libraries are also Bitcode-enabled, as this could affect the use of the `ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES` setting.