Key takeaways
Static linking: The compiler includes the code in the executable, offering faster runtime performance but larger binary sizes.
Dynamic linking: Libraries are loaded at runtime, supporting resource bundling (images, fonts) and reducing initial app load time.
File formats: Static libraries typically use the
.aextension, while dynamic libraries use.dylib.Swift benefits: Dynamic frameworks support module stability, allowing updates without recompiling the entire application.
Use case: Choose static for performance-critical code and dynamic for modular apps requiring shared resources.
Understanding static and dynamic linking
Here is a comparison that will help you understand the differences between static and dynamic linking.
Static linker (ld)
During compile time, the static linker includes all the code from the static library in the final executable. This means that once the app is compiled, it contains all the necessary code and is self-sufficient.
Dynamic linker (dyld)
At load or run time, the dynamic linker finds the embedded framework using @rpath and links it to the executable. This lets the app load the library only when needed, saving memory and reducing the application's initial load time.
File extensions
Library type | File extension |
|---|---|
Static Library |
|
Dynamic library |
|
Dynamic frameworks are particularly useful because they allow you to include resources such as fonts, images, XIBs, and storyboards. You can access these resources using the framework’s bundle identifier, which makes resource management much easier.
Defining framework types
When creating a framework, decide whether it will be static or dynamic. Here’s how to distinguish between the two:
Static libraries
Linked at compile time: All code from the static library is included in the app’s final binary at compile time. This results in faster runtime performance when accessing the library’s code.
Performance: Since everything is compiled into a single binary, the app runs faster because it doesn't need to load additional code at runtime.
Content: Static libraries contain only code. While it is technically possible to include resources in base64 format, it is not advisable because of the added complexity and potential performance issues.
Dynamic libraries
Linked at runtime: The library code loads into memory only when needed, which can reduce the application's initial load time.
Performance: While the app launches faster, accessing code in a dynamic library is slower than in a static library because of the additional overhead of loading the library at runtime.
Content: Dynamic libraries can include both code and resources. This makes them ideal for frameworks that need to bundle multiple asset types.
Executable: All iOS applications fall under this category. The executable is the main file that runs when the app is launched.
Bundle: Used solely for storing resources such as fonts, images, XIBs, storyboards, and Core Data models. Bundles do not contain executable code.
Framework: A combination of static libraries and bundles, or dynamic libraries. This flexibility lets you choose the best approach for your project.
Pros and cons
Feature | Static frameworks | Dynamic frameworks |
|---|---|---|
Linking Time | Compile time | Runtime / Load time |
Binary size | Larger (code embedded) | Smaller (linked externally) |
Resources | Code only (mostly) | Code and Assets (Images, Xibs) |
Performance | Faster runtime | Faster launch, overhead at runtime |
Use cases and considerations
When deciding between static and dynamic frameworks, consider the following use cases:
Static frameworks: Best suited for performance-critical applications where the fastest possible runtime performance is required. They are also ideal for simple libraries that don't need to bundle resources or update independently.
Dynamic frameworks: Ideal for complex applications that require modular updates or where multiple resources need to be managed. They are also beneficial when you need to share common code across different projects or teams without duplicating resources.
Best practices
Minimize dependencies: Whether using static or dynamic libraries, aim to minimize dependencies to reduce complexity and potential conflicts.
Optimize resource management: For dynamic frameworks, ensure that resources are properly organized and accessed efficiently using the framework’s bundle identifier.
Consider app size: Be mindful of the impact on app size. While dynamic libraries can reduce initial load time, they can increase the overall size of the app package because of bundled resources.
In conclusion, the choice between static and dynamic frameworks depends on your project’s specific needs for performance, resource management, and update flexibility. Understanding the differences and carefully considering the pros and cons will help you make the best decision for your application.
