Understanding Static and Dynamic Libraries: A Deep Dive for iOS Developers 🚀

credit: https://imageupscaler.com/

Introduction

As iOS developers, memory management and efficient app bundling are crucial for delivering high-performance apps. This article explores the differences between static and dynamic libraries, their impact on executable size, and overall app size, using relatable examples and practical insights. Whether you’re a budding developer or a seasoned lead, this guide will help you understand how these libraries work and how to optimise your app’s performance. 🌟

Static Libraries 📚

What Are Static Libraries?

Static libraries are collections of object files bundled together. When you link a static library to your app, the library’s code is copied directly into your executable at compile time.

Key Characteristics

• Executable Size: Larger because the code from the static library is embedded directly into the executable.
• Total App Size: Includes the larger executable plus all other resources, leading to a monolithic executable file.

Example

// Imagine you have a static library of 1MB
let appExecutableSize = 5MB // Base app
let staticLibrarySize = 1MB // Static library
let totalExecutableSize = appExecutableSize + staticLibrarySize // 6MB
let otherResources = 10MB // Images, sounds, etc.
let totalAppSize = totalExecutableSize + otherResources // 16MB

Dynamic Libraries 📂

What Are Dynamic Libraries?

Dynamic libraries, on the other hand, are linked to your app at runtime. The executable contains only references to the dynamic library, and the actual code is loaded when the app runs.

Key Characteristics

• Executable Size: Smaller because it includes only references to the dynamic library.
• Total App Size: Includes the smaller executable plus the dynamic library files, which are part of the app bundle but separate from the executable.

Example

// Imagine you have a dynamic library of 1MB
let appExecutableSize = 5MB // Base app
let dynamicLibraryReference = negligible // Small reference
let totalExecutableSize = appExecutableSize + dynamicLibraryReference // Slightly more than 5MB
let dynamicLibraryFileSize = 1MB // Dynamic library file
let otherResources = 10MB // Images, sounds, etc.
let totalAppSize = totalExecutableSize + dynamicLibraryFileSize + otherResources // Slightly more than 16MB

Frameworks

• Definition: A framework is a structured package that can include static or dynamic libraries, along with other resources like headers, images, and documentation.
• File Extension: Typically .framework on macOS/iOS.
• Contents: A framework encapsulates both the code (as a static or dynamic library) and resources, providing a modular and reusable component.

Where to find in Xcode

To determine whether a framework is added as a static or dynamic library in your project:

1. Navigate to the Target Settings: In Xcode, select your project from the Project Navigator, and then select the specific target you’re interested in.
2. Open Build Settings: Go to the “Build Settings” tab for the selected target.
3. Search for Mach-O Type: Use the search bar in the Build Settings to look for “Mach-O Type”. The value shown here will indicate whether the framework is being treated as a static library (Static Library) or a dynamic library (Dynamic Library).

Comparing Static vs. Dynamic Libraries ⚖️

Executable Size

• Static Libraries: Larger executable due to embedded code.
• Dynamic Libraries: Smaller executable with external references.

Total App Size

• Static Libraries: Total app size includes a larger executable.
• Dynamic Libraries: Total app size includes a smaller executable and separate dynamic library files.

Practical Implications

1. Memory Management: Dynamic libraries can be shared across multiple apps, reducing memory usage.
2. Modularity: Dynamic libraries promote better modularity and easier updates.

Conclusion 🎉

Understanding the differences between static and dynamic libraries is crucial for optimising your iOS app’s performance. While static libraries increase the executable size by embedding code, dynamic libraries keep the executable smaller by referencing external files. However, the total app size remains similar in both cases as it includes all necessary resources and libraries.

By choosing the right type of library and managing them effectively, you can ensure better performance, memory management, and modularity in your apps. Happy coding! 👩‍💻👨‍💻

Feedback and Discussion 💬

Have you encountered challenges with static or dynamic libraries in your iOS projects? What strategies have you found most effective for optimising app size and performance? Share your thoughts and experiences in the comments below! Let’s learn and grow together. 🚀

References

• Doc