Add support for storing Id and Box in ivars

Author: madsmtm

objc2/CHANGELOG.md

@@ -8,8 +8,11 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ## Unreleased - YYYY-MM-DD
 
 ### Added
-* `Ivar::write`, `Ivar::as_ptr` and `Ivar::as_mut_ptr` for querying/modifying
-  the instance variable inside `init` methods.
+* Added `Ivar::write`, `Ivar::as_ptr` and `Ivar::as_mut_ptr` for safely
+  querying and modifying instance variables inside `init` methods.
+* Added `IvarDrop<T>` to allow storing complex `Drop` values in ivars
+  (currently `rc::Id<T, O>`, `Box<T>`, `Option<rc::Id<T, O>>` or
+  `Option<Box<T>>`).
 
 ### Removed
 * **BREAKING**: `MaybeUninit` no longer implements `IvarType` directly; use

objc2/examples/delegate.rs

@@ -1,9 +1,9 @@
 #![cfg_attr(not(all(feature = "apple", target_os = "macos")), allow(unused))]
-use objc2::declare::Ivar;
-use objc2::foundation::NSObject;
+use objc2::declare::{Ivar, IvarDrop};
+use objc2::foundation::{NSCopying, NSObject, NSString};
 use objc2::rc::{Id, Shared};
 use objc2::runtime::Object;
-use objc2::{declare_class, extern_class, msg_send, msg_send_id, ClassType};
+use objc2::{declare_class, extern_class, msg_send, msg_send_id, ns_string, ClassType};
 
 #[cfg(all(feature = "apple", target_os = "macos"))]
 #[link(name = "AppKit", kind = "framework")]
@@ -23,6 +23,10 @@ declare_class!(
     struct CustomAppDelegate {
         pub ivar: u8,
         another_ivar: bool,
+        box_ivar: IvarDrop<Box<i32>>,
+        maybe_box_ivar: IvarDrop<Option<Box<i32>>>,
+        id_ivar: IvarDrop<Id<NSString, Shared>>,
+        maybe_id_ivar: IvarDrop<Option<Id<NSString, Shared>>>,
     }
 
     unsafe impl ClassType for CustomAppDelegate {
@@ -34,18 +38,28 @@ declare_class!(
         #[sel(initWith:another:)]
         fn init_with(self: &mut Self, ivar: u8, another_ivar: bool) -> Option<&mut Self> {
             let this: Option<&mut Self> = unsafe { msg_send![super(self), init] };
+
+            // TODO: `ns_string` can't be used inside closures; investigate!
+            let s = ns_string!("def");
+
             this.map(|this| {
+                // Initialize instance variables
+
+                // The explicit way to initialize an instance variable:
                 Ivar::write(&mut this.ivar, ivar);
-                Ivar::write(&mut this.another_ivar, another_ivar);
-                // Note that we could have done this with just:
-                // *this.ivar = ivar;
-                // *this.another_ivar = another_ivar;
-                //
-                // Since these two ivar types (`u8` and `bool`) are safe to
-                // initialize from all zeroes; but for this example, we chose
-                // to be explicit.
-
-                // SAFETY: All the instance variables have been initialized
+                // For some types like `u8`, `bool`, `Option<Box<T>>` and
+                // `Option<Id<T, O>>` which are safe to zero-initialize, we
+                // can simply write to the variable as normal:
+                *this.another_ivar = another_ivar;
+                *this.maybe_box_ivar = None;
+                *this.maybe_id_ivar = Some(s.copy());
+                // While for others like `&u8`, `Box<T>` or `Id<T, O>`, we
+                // have to initialize it with `Ivar::write`:
+                Ivar::write(&mut this.box_ivar, Box::new(2));
+                Ivar::write(&mut this.id_ivar, NSString::from_str("abc"));
+
+                // All the instance variables have been initialized; our
+                // initializer is sound
                 this
             })
         }
@@ -97,8 +111,12 @@ impl CustomAppDelegate {
 fn main() {
     let delegate = CustomAppDelegate::new(42, true);
 
-    println!("{}", delegate.ivar);
-    println!("{}", delegate.another_ivar);
+    println!("{:?}", delegate.ivar);
+    println!("{:?}", delegate.another_ivar);
+    println!("{:?}", delegate.box_ivar);
+    println!("{:?}", delegate.maybe_box_ivar);
+    println!("{:?}", delegate.id_ivar);
+    println!("{:?}", delegate.maybe_id_ivar);
 }
 
 #[cfg(not(all(feature = "apple", target_os = "macos")))]

objc2/src/__macro_helpers.rs

@@ -13,6 +13,7 @@ pub use core::mem::size_of;
 pub use core::ops::{Deref, DerefMut};
 pub use core::option::Option::{self, None, Some};
 pub use core::primitive::{bool, str, u8};
+pub use core::ptr::drop_in_place;
 pub use core::{compile_error, concat, panic, stringify};
 // TODO: Use `core::cell::LazyCell`
 pub use std::sync::Once;

objc2/src/declare.rs

@@ -112,6 +112,7 @@
 //! ```
 
 mod ivar;
+mod ivar_drop;
 mod ivar_forwarding_impls;
 
 use alloc::format;
@@ -122,13 +123,14 @@ use core::ptr;
 use core::ptr::NonNull;
 use std::ffi::CString;
 
-use crate::encode::{Encode, EncodeArguments, EncodeConvert, Encoding, RefEncode};
+use crate::encode::{Encode, EncodeArguments, Encoding, RefEncode};
 use crate::ffi;
 use crate::runtime::{Bool, Class, Imp, Object, Protocol, Sel};
 use crate::sel;
 use crate::Message;
 
-pub use ivar::{Ivar, IvarType};
+pub use ivar::{InnerIvarType, Ivar, IvarType};
+pub use ivar_drop::IvarDrop;
 
 pub(crate) mod private {
     pub trait Sealed {}
@@ -439,7 +441,12 @@ impl ClassBuilder {
     /// Same as [`ClassBuilder::add_ivar`].
     pub fn add_static_ivar<T: IvarType>(&mut self) {
         // SAFETY: The encoding is correct
-        unsafe { self.add_ivar_inner::<T::Type>(T::NAME, &T::Type::__ENCODING) }
+        unsafe {
+            self.add_ivar_inner::<<T::Type as InnerIvarType>::__Inner>(
+                T::NAME,
+                &T::Type::__ENCODING,
+            )
+        }
     }
 
     /// Adds the given protocol to self.