go-macos/objc

A pure-Go (CGO_ENABLED=0) bridge to the macOS Objective-C runtime, reached entirely through ebitengine/purego — dlopen + objc_msgSend, no cgo, no shelling out to osascript.

It is the single shared home for the Objective-C plumbing that the fleet's CGO=0 macOS code kept re-implementing: selector/class lookup, NSString↔Go bridging, framework dlopen, autorelease-pool handling and run loops.

Surface

Area	API
Selector / class lookup (cached)	Sel, RegisterName, GetClass, ClassID
Messaging	ID.Send, generic Send[T] (scalars, CGFloat, structs)
Runtime classes	RegisterClass, RegisterClassWithProtocols, GetProtocol, MethodDef
Strings	NSString, GoString
Objects / dictionaries	Stringify, DictToMap, MapToDict
Frameworks	Load + Foundation / AppKit / WebKit / CoreFoundation / Security / LibSystem
Scopes	AutoreleasePool
Run loops	App, RunApp, Run(ctx, class, setup) + Runner
Validation	ValidateName

import "github.com/go-macos/objc"

objc.Load(objc.Foundation, objc.AppKit)

s := objc.GoString(objc.NSString("héllo"))                 // "héllo"
n := objc.Send[float64](objc.NSString("3.5"), objc.Sel("doubleValue")) // 3.5

cls, _ := objc.RegisterClass("MyTarget", objc.GetClass("NSObject"),
    []objc.MethodDef{
        {Cmd: objc.Sel("fire:"), Fn: func(self objc.ID, _ objc.SEL, sender objc.ID) {
            // handle sender
        }},
    })

Design

• On darwin the runtime types (ID, SEL, Class, IMP, MethodDef) are aliases of the corresponding purego/objc types, so method closures satisfy purego's strict NewIMP (id, SEL) receiver check and existing purego-based call sites can switch their import to this package and keep compiling.
• On non-darwin the same symbols exist as uintptr-width types and stubs that report [ErrUnsupported], so consumers cross-compile. The OS-independent core (selector/class caches, name validation, the GoString marshalling logic and Load) stays fully functional and is covered 100% on every lane through injection seams.
• The darwin C/objc calls sit behind fake-injection seams, so their error branches are reachable in tests; the real objc_msgSend / NSString / RegisterClass / run-loop paths are verified on-device in CI.

License

BSD-3-Clause © the go-macos/objc authors.