Add autoreleasepool functionality.

This replicates the behaviour of @autoreleasepool blocks in
Objective-C and allows higher performance creation of autorelease pools.

src/autorelease.rs

@@ -0,0 +1,39 @@
+use std::os::raw::c_void;
+use runtime::{objc_autoreleasePoolPush, objc_autoreleasePoolPop};
+
+// we use a struct to ensure that objc_autoreleasePoolPop during unwinding.
+struct AutoReleaseHelper {
+    context: *mut c_void,
+}
+
+impl AutoReleaseHelper {
+    unsafe fn new() -> Self {
+        AutoReleaseHelper { context: objc_autoreleasePoolPush() }
+    }
+}
+
+impl Drop for AutoReleaseHelper {
+    fn drop(&mut self) {
+        unsafe { objc_autoreleasePoolPop(self.context) }
+    }
+}
+
+/**
+Execute `f` in the context of a new autorelease pool. The pool is drained
+after the execution of `f` completes. This corresponds to @autoreleasepool blocks
+in Objective-c and Swift.
+*/
+pub fn autoreleasepool<F: FnOnce()>(f: F) {
+    let _context = unsafe { AutoReleaseHelper::new() };
+    f();
+}
+
+#[cfg(test)]
+mod tests {
+    use super::autoreleasepool;
+
+    #[test]
+    fn test_pool() {
+        autoreleasepool(|| {});
+    }
+}

src/lib.rs

@@ -75,6 +75,8 @@ mod macros;
 
 pub mod runtime;
 pub mod declare;
+mod autorelease;
+pub use autorelease::autoreleasepool;
 mod encode;
 #[cfg(feature = "exception")]
 mod exception;

src/runtime.rs

@@ -109,6 +109,9 @@ extern {
     pub fn objc_allocateProtocol(name: *const c_char) -> *mut Protocol;
     pub fn objc_registerProtocol(proto: *mut Protocol);
 
+    pub fn objc_autoreleasePoolPush() -> *mut c_void;
+    pub fn objc_autoreleasePoolPop(context: *mut c_void);
+
     pub fn protocol_addMethodDescription(proto: *mut Protocol, name: Sel, types: *const c_char, isRequiredMethod: BOOL,
                                          isInstanceMethod: BOOL);
     pub fn protocol_addProtocol(proto: *mut Protocol, addition: *const Protocol);