sx/library/modules/ffi/objc.sx

// Obj-C runtime FFI primitives.
//
// objc_msgSend has the standard ARM64 calling convention (no varargs path).
// Each call site must invoke through a function pointer of the *exact*
// argument and return shape. The idiom:
//
//     msg_fn : (recv: *void, sel: *void, arg: [*]u8) -> *void = xx objc_msgSend;
//     result := msg_fn(receiver, selector, c_str);

// ─── Obj-C primitive type aliases ───────────────────────────────────────
// Named stand-ins for the three opaque Obj-C runtime types. They all
// resolve to `*void` at the LLVM layer (no runtime cost) but improve
// readability in foreign-class declarations and call sites.
//
//   id    — any Obj-C instance pointer
//   Class — a class object pointer
//   SEL   — a registered selector
//
// `Class(T)` parameterization (phantom-typed, with `#extends`-aware
// covariance) is a follow-up — needs compiler-level type-check support.
// For now, `Class` alone is the only form; assignments are not checked
// against the referent's class hierarchy.
id    :: *void;
Class :: *void;
SEL   :: *void;

// Apple's `BOOL` is a signed char (NOT sx's built-in `bool`, which is
// LLVM `i1`). Obj-C method signatures that take or return `BOOL` cross
// the FFI boundary as `i8`.
BOOL :: i8;

// On macOS libobjc is auto-loaded by libSystem; on iOS it isn't, so we
// link it explicitly. Foundation registers NSString etc. with the runtime,
// also auto-loaded on macOS and required as an explicit framework on iOS.
objc :: #library "objc";
#framework "Foundation";

objc_getClass         :: (name: [*]u8)                  -> *void  #foreign objc;
objc_lookUpClass      :: (name: [*]u8)                  -> *void  #foreign objc;
sel_registerName      :: (name: [*]u8)                  -> *void  #foreign objc;
class_createInstance  :: (cls: *void, extra: usize)     -> *void  #foreign objc;
object_getClass       :: (obj: *void)                   -> *void  #foreign objc;
object_getIvar        :: (obj: *void, ivar: *void)      -> *void  #foreign objc;
object_setIvar        :: (obj: *void, ivar: *void, val: *void)    #foreign objc;

// Declared with the simplest non-variadic shape. Cast per call site.
objc_msgSend          :: (recv: *void, sel: *void)      -> *void  #foreign objc;

// ─── Dynamic class registration ─────────────────────────────────────────
// Define a new Obj-C class at runtime: allocate the pair, attach methods +
// protocols, then finalize with `objc_registerClassPair`. The class is then
// usable via `class_createInstance` and Obj-C dispatch.
//
// IMPs (method implementations) are function pointers with the implicit
// Obj-C method shape: `(self: *void, _cmd: *void, ...args) -> ret` with
// `callconv(.c)` so they land args in the standard C registers.
//
// Method type encoding strings follow Apple's runtime DSL:
//   v = void   c = char/BOOL   i = int   l = long   f = float   d = double
//   @ = id (object)            : = SEL                # = Class
// Return type comes first, then receiver (`@`), then `_cmd` (`:`), then args.
// Examples:
//   "v@:"     -> void   method(id, SEL)
//   "c@:"     -> BOOL   method(id, SEL)
//   "@@:@"    -> id     method(id, SEL, id)
//   "B@:@@"   -> BOOL   method(id, SEL, id, id)
objc_allocateClassPair :: (super: *void, name: [*]u8, extra: usize) -> *void  #foreign objc;
class_addMethod        :: (cls: *void, sel: *void, imp: *void, types: [*]u8) -> bool   #foreign objc;
class_addProtocol      :: (cls: *void, proto: *void)                          -> bool   #foreign objc;
objc_getProtocol       :: (name: [*]u8)                                       -> *void  #foreign objc;
objc_registerClassPair :: (cls: *void)                                        -> void   #foreign objc;

// Foundation C-API helpers (Foundation is already linked above via #framework).
// NSLog takes an NSString format; the variadic tail is not exposed here.
NSLog :: (fmt: *NSString) #foreign;

// ─── NSObject (Phase 4 / M4.A) ───────────────────────────────────────────
// Root of every Obj-C class hierarchy. Apple's runtime supplies the IMPs;
// sx declares the method surface so user code can write
// `defer view.release();` and `view.retain()` directly instead of going
// through `objc_msgSend` casts. M2.3's `#extends`-aware dispatch finds
// these methods automatically once a class roots its `#extends` chain at
// NSObject (foreign classes in uikit.sx etc. add `#extends NSObject;` to
// inherit the surface).
//
// `release` is NOT a reserved keyword in sx — modern clang ARC bans
// user-source calls to it (the ARC compiler emits them automatically), but
// sx isn't under clang ARC. Calling `view.release()` here is equivalent to
// pre-ARC Obj-C source code: dispatches through the runtime, decrements the
// refcount, fires `-dealloc` at zero.
NSObject :: #foreign #objc_class("NSObject") {
    alloc       :: () -> *NSObject;
    init        :: (self: *Self) -> *NSObject;
    new         :: () -> *NSObject;       // shorthand for [[Cls alloc] init]
    retain      :: (self: *Self) -> *Self;
    release     :: (self: *Self);
    autorelease :: (self: *Self) -> *Self;
    class       :: () -> *void;            // metaclass query — `Cls.class()`
    description :: (self: *Self) -> *void;  // returns *NSString
    hash        :: (self: *Self) -> u64;
    isEqual         :: (self: *Self, other: *void) -> BOOL;
    isKindOfClass   :: (self: *Self, cls: *void) -> BOOL;
    respondsToSelector :: (self: *Self, sel: *void) -> BOOL;
}

// ─── NSString ────────────────────────────────────────────────────────────
// Foundation's immutable string. `UTF8String` views the bytes as a C string
// whose lifetime is tied to the NSString (don't free it). The `Into` impl
// lets a string literal flow into any `*NSString` slot via `xx`, e.g.
// `dict.objectForKey(xx "SomeKey")`.
NSString :: #foreign #objc_class("NSString") {
    #extends NSObject;
    UTF8String :: (self: *Self) -> [*]u8;
}

// Wraps the bytes in an autoreleased NSString via `+stringWithUTF8String:`.
// `self.ptr` must be NUL-terminated — string literals are; an arbitrary
// sliced/built `string` may not be.
impl Into(*NSString) for string {
    convert :: (self: string) -> *NSString {
        cls := objc_getClass("NSString".ptr);
        sel := sel_registerName("stringWithUTF8String:".ptr);
        msg : (*void, *void, [*]u8) -> *void callconv(.c) = xx objc_msgSend;
        return xx msg(cls, sel, self.ptr);
    }
}

// ─── Autoreleasepool (M4.A) ──────────────────────────────────────────────
// Foundation factory methods (`NSString.stringWithUTF8String:`,
// `[NSArray array]`, ...) return autoreleased objects — valid until the
// current pool drains. Wrap such code in `autoreleasepool(() => { ... })`
// so the pool drains deterministically at block end.
//
// Stdlib helper, not a language keyword. The closure call adds a frame —
// for hot loops, inline the push/defer-pop pattern manually.

objc_autoreleasePoolPush :: ()                  -> *void  #foreign objc;
objc_autoreleasePoolPop  :: (pool: *void)                 #foreign objc;

autoreleasepool :: (body: Closure()) {
    pool := objc_autoreleasePoolPush();
    defer objc_autoreleasePoolPop(pool);
    body();
}