.so vs. .dylib in macOS: When to Use Which Shared Library Type?

Understanding the Distinctions between .so and .dylib in macOS

Conceptual Differences

Mach-O, the object file format in macOS, differentiates between shared libraries (.dylib) and dynamically loaded modules (bundles). Shared libraries are linked during compilation and can be referenced using -lfoo flags. Bundles, on the other hand, are plug-ins that extend applications and link against their exported API.

When to Use One Over the Other

• Shared libraries (dylibs) are suitable for components that are linked statically and accessed through the standard linker.
• Bundles (with any extension, often .so for compatibility) are useful for plug-ins that extend an application's functionality.

Compilation Considerations

• To create a shared library (dylib), use -dynamiclib.
• To build a loadable bundle, use -bundle.

Historical Context

In early macOS versions, bundles were used for dynamic loading, while dylibs were introduced later. However, with macOS 10.5, both dylibs and bundles could be dynamically loaded using the dl APIs.

Note on Bundles in macOS

"Bundle" can also refer to directories with standardized structures containing code and resources. This concept is similar to Mach-O bundles used as plugins, but they should not be confused with each other.

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