objc2 is a Rust library that provides safe, idiomatic bindings to Apple's Objective-C runtime and a vast portion of its system frameworks (Foundation, AppKit, Metal, CoreFoundation, and hundreds more). The core crate wraps the Objective-C runtime with type-safe message sending, class definition, reference counting via Retained<T>, and protocol support. Around it, the workspace includes supporting crates for Objective-C blocks (block2), Grand Central Dispatch (dispatch2), a header translator that auto-generates Rust code from Apple's SDK headers, and a documentation parser (apple-doc). The architecture is a large Rust workspace (hundreds of crates) with a clear separation: a lightweight runtime layer (objc2-encode, objc2-exception-helper, objc2-proc-macros), the main objc2 crate with macros and runtime types, and generated framework crates that follow a uniform pattern (extern_class!, extern_methods!, etc.). The project places heavy emphasis on safety and correctness, employing compile-time encoding verification, fuzz testing, assembly-level baseline tests for optimized message sending, and UI tests to catch type errors at compile time. Despite its complexity, the code exhibits strong craftsmanship: the macro infrastructure is well-organized, memory management is carefully designed (two-phase initialization, drop flags, Writeback helpers), and performance-critical paths use inline assembly for retain/autorelease optimization. The project is actively maintained with a modern toolchain, CI against multiple runtimes (Apple, GNUstep, ObjFW), and thorough documentation. It stands as the most comprehensive Rust-to-Objective-C bridge available, suitable for building native macOS/iOS applications entirely in Rust.
The GNUstep Base Library is a portable, open-source reimplementation of Apple's Foundation framework, providing the core non-graphical Objective-C classes for strings, collections, networking, serialization, date/time handling, and more. It serves as the foundational library for the GNUstep ecosystem, enabling cross-platform development on Unix, Windows, and Android. The library is monolithic in structure, with a public API mirroring Apple's Foundation headers and internal implementation modules for platform-specific concerns (e.g., threading, sockets, dynamic loading). Key entry points include the umbrella header Foundation.h and root classes like NSObject, NSString, and NSArray. External dependencies include libobjc2 (Objective-C runtime), ICU (Unicode), libxml2 (XML), libcurl (URL loading), and GnuTLS (TLS). The codebase is extensive and well-tested, but contains many stub implementations for newer macOS APIs and legacy compatibility layers, reflecting its long history and broad platform support.