objrs_runtime 0.0.2

Bindings for Apple's libobjc runtime for objrs.
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// The contents of this file is licensed by its authors and copyright holders under the Apache
// License (Version 2.0), MIT license, or Mozilla Public License (Version 2.0), at your option. The
// contents of this file may not be copied, modified, or distributed except according to those
// terms. See the COPYRIGHT file at the top-level directory of this distribution for copies of these
// licenses and more information.

// See https://github.com/opensource-apple/objc4/blob/master/runtime/objc-internal.h
// and https://clang.llvm.org/docs/AutomaticReferenceCounting.html

extern crate core;
extern crate libc;

use objc;

#[link(name = "objc")]
extern "C" {
  pub fn objc_autoreleasePoolPush() -> *mut libc::c_void;
  pub fn objc_autoreleasePoolPop(pool: *mut libc::c_void);

  pub fn objc_retain(obj: objc::id) -> objc::id;
  pub fn objc_release(obj: objc::id);
  pub fn objc_autorelease(obj: objc::id) -> objc::id;
  pub fn objc_retainAutorelease(obj: objc::id) -> objc::id;

  pub fn objc_loadWeakRetained(location: *mut objc::id) -> objc::id;
}

// TODO: I think that this macro should be removed. Consider the following code:
// fn do_stuff() {
//   autoreleasepool!{
//     return;
//   }
// }
// I believe the return statement would result in the autoreleasepool not being popped.
// This could possibly be fixed by using a gaurd variable with a Drop implementation that pops the pool, but I'm not sure that's foolproof.
// #[macro_export]
// macro_rules! autoreleasepool {
//   ($($tt: tt)*) => {
//     // Compiling the Objective-C program `int main() {@autoreleasepool{} return 0;}` shows that
//     // clang doesn't check the return value of the pool push. If clang never does it, then I feel
//     // comfortable not doing it here either (plus I've looked through the Objective-C runtime code
//     // and I don't think our lack of null-checking here can be problematic).
//     // TODO: does this need to be surrounded in {} for any reason?
//     let pool = unsafe { objc_autoreleasePoolPush() };
//     {$($tt)*;}
//     unsafe { objc_autoreleasePoolPop(pool) };
//   };
// }

// TODO: What happens to autoreleasepools when an exception is thrown (before the pool is popped)? How does Objective-C handle it, and does objrs match it?
// We only take Fn instead of FnOnce or FnMut in order to avoid allowing the user to accidentally create dangling references to autoreleased values.
#[inline(always)]
pub fn autoreleasepool<F: Fn()>(f: F) {
  let pool = unsafe { objc_autoreleasePoolPush() };
  f();
  unsafe { objc_autoreleasePoolPop(pool) };
}