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/// Create a new type to represent a class.
///
/// This is similar to an `@interface` declaration in Objective-C.
///
/// It is useful for things like `objc2-foundation`, which needs to create
/// interfaces to existing, externally defined classes like `NSString`,
/// `NSURL` and so on, but can also be useful for users that have custom
/// classes written in Objective-C that they want to access from Rust.
///
///
/// # Specification
///
/// The syntax is similar enough to Rust syntax that if you invoke the macro
/// with parentheses (as opposed to curly brackets), [`rustfmt` will be able to
/// format the contents][rustfmt-macros] (so e.g. as `extern_class!( ... );`).
///
/// The macro creates an opaque struct containing the superclass (which means
/// that auto traits are inherited from the superclass), and implements the
/// following traits for it to allow easier usage as an Objective-C object:
///
/// - [`RefEncode`][crate::RefEncode]
/// - [`Message`][crate::Message]
/// - [`ClassType`][crate::ClassType]
/// - [`Deref<Target = $superclass>`][core::ops::Deref]
/// - [`DerefMut`][core::ops::DerefMut]
/// - [`AsRef<$inheritance_chain>`][AsRef]
/// - [`AsMut<$inheritance_chain>`][AsMut]
/// - [`Borrow<$inheritance_chain>`][core::borrow::Borrow]
/// - [`BorrowMut<$inheritance_chain>`][core::borrow::BorrowMut]
///
/// The macro allows specifying zero-sized fields like [`PhantomData`] on the
/// struct.
///
/// You can add most attributes to the class, including `#[cfg(...)]`,
/// `#[derive(...)]` and doc comments (but not ABI-modifying attributes like
/// `#[repr(...)]`).
///
/// [rustfmt-macros]: https://github.com/rust-lang/rustfmt/discussions/5437
/// [`PhantomData`]: core::marker::PhantomData
///
///
/// ## `ClassType` implementation
///
/// The syntax of this macro neatly documents that it implements the
/// [`ClassType`] trait for you, though to do so you need to provide it the
/// following:
/// - The [`Super`] class.
///
/// Due to Rust trait limitations, specifying e.g. the superclass `NSData`
/// would not give you the ability to convert via. `AsRef` to `NSObject`.
/// Therefore, you may optionally specify additional parts of the
/// inheritance chain using an `#[inherits(...)]` attribute.
/// - The class' [`Mutability`].
/// - Optionally, the class' [`NAME`] - if not specified, this will default to
/// the struct name.
///
/// You may add `#[cfg(...)]` attributes to the `ClassType` impl, and then it
/// will work as expected. No other attributes are supported.
///
/// [`ClassType`]: crate::ClassType
/// [`Super`]: crate::ClassType::Super
/// [`Mutability`]: crate::ClassType::Mutability
/// [`NAME`]: crate::ClassType::NAME
///
///
/// # Safety
///
/// This macro implements the three unsafe traits [`RefEncode`], [`Message`]
/// and [`ClassType`] for you, and while it can ensure most of the required
/// properties in those, it cannot ensure all of them.
///
/// In particular, when writing `unsafe` on `impl ClassType`, you must ensure
/// that:
/// 1. [`ClassType::Super`] is correct.
/// 2. [`ClassType::Mutability`] is correct.
///
/// See [`ClassType`'s safety section][ClassType#safety] for further
/// details on what this entails.
///
/// [`RefEncode`]: crate::encode::RefEncode
/// [`Message`]: crate::Message
/// [`ClassType::Super`]: crate::ClassType::Super
/// [`ClassType::Mutability`]: crate::ClassType::Mutability
/// [ClassType#safety]: crate::ClassType#safety
///
///
/// # Examples
///
/// Create a new type to represent the `NSFormatter` class (for demonstration,
/// `objc2_foundation::NSFormatter` exist for exactly this purpose).
///
/// ```
/// # #[cfg(not_available)]
/// use objc2_foundation::{NSCoding, NSCopying, NSObjectProtocol};
/// # use objc2::runtime::NSObjectProtocol;
/// use objc2::rc::Retained;
/// use objc2::runtime::NSObject;
/// use objc2::{extern_class, msg_send_id, mutability, ClassType};
///
/// extern_class!(
/// /// An example description.
/// #[derive(PartialEq, Eq, Hash)] // Uses the superclass' implementation
/// // Specify the class and struct name to be used
/// pub struct NSFormatter;
///
/// // Specify the superclass, in this case `NSObject`
/// unsafe impl ClassType for NSFormatter {
/// type Super = NSObject;
/// type Mutability = mutability::InteriorMutable;
/// // Optionally, specify the name of the class, if it differs from
/// // the struct name.
/// // const NAME: &'static str = "NSFormatter";
/// }
/// );
///
/// // Note: We have to specify the protocols for the superclasses as well,
/// // since Rust doesn't do inheritance.
/// unsafe impl NSObjectProtocol for NSFormatter {}
/// # #[cfg(not_available)]
/// unsafe impl NSCopying for NSFormatter {}
/// # #[cfg(not_available)]
/// unsafe impl NSCoding for NSFormatter {}
///
/// fn main() {
/// // Provided by the implementation of `ClassType`
/// let cls = NSFormatter::class();
///
/// // `NSFormatter` implements `Message`:
/// let obj: Retained<NSFormatter> = unsafe { msg_send_id![cls, new] };
/// }
/// ```
///
/// Represent the `NSDateFormatter` class, using the `NSFormatter` type we
/// declared previously to specify as its superclass.
///
/// ```
/// # #[cfg(not_available)]
/// use objc2_foundation::{NSCoding, NSCopying, NSObjectProtocol};
/// # use objc2::runtime::NSObjectProtocol;
/// use objc2::runtime::NSObject;
/// use objc2::{extern_class, mutability, ClassType};
/// #
/// # extern_class!(
/// # #[derive(PartialEq, Eq, Hash)]
/// # pub struct NSFormatter;
/// #
/// # unsafe impl ClassType for NSFormatter {
/// # type Super = NSObject;
/// # type Mutability = mutability::InteriorMutable;
/// # }
/// # );
///
/// extern_class!(
/// #[derive(PartialEq, Eq, Hash)]
/// pub struct NSDateFormatter;
///
/// unsafe impl ClassType for NSDateFormatter {
/// // Specify the correct inheritance chain
/// #[inherits(NSObject)]
/// type Super = NSFormatter;
/// type Mutability = mutability::InteriorMutable;
/// }
/// );
///
/// // Similarly, we can specify the protocols that this implements here:
/// unsafe impl NSObjectProtocol for NSFormatter {}
/// # #[cfg(not_available)]
/// unsafe impl NSCopying for NSDateFormatter {}
/// # #[cfg(not_available)]
/// unsafe impl NSCoding for NSDateFormatter {}
/// ```
///
/// See the source code of `objc2-foundation` for many more examples.
#[doc(alias = "@interface")]
#[macro_export]
macro_rules! extern_class {
// No fields
(
$(#[$m:meta])*
$v:vis struct $name:ident;
$(#[$impl_m:meta])*
unsafe impl ClassType for $for:ty {
$(#[inherits($($inheritance_rest:ty),+)])?
type Super = $superclass:ty;
type Mutability = $mutability:ty;
$(const NAME: &'static str = $name_const:expr;)?
}
) => {
// Shorthand syntax for the following
$crate::extern_class!(
$(#[$m])*
$v struct $name {}
$(#[$impl_m])*
unsafe impl ClassType for $for {
$(#[inherits($($inheritance_rest),+)])?
type Super = $superclass;
type Mutability = $mutability;
$(const NAME: &'static str = $name_const;)?
}
);
};
(
$(#[$m:meta])*
$v:vis struct $name:ident {
$($field_vis:vis $field:ident: $field_ty:ty,)*
}
$(#[$impl_m:meta])*
unsafe impl ClassType for $for:ty {
$(#[inherits($($inheritance_rest:ty),+)])?
type Super = $superclass:ty;
type Mutability = $mutability:ty;
$(const NAME: &'static str = $name_const:expr;)?
}
) => {
$crate::__inner_extern_class!(
$(#[$m])*
$v struct $name<> {
__superclass: $superclass,
$($field_vis $field: $field_ty,)*
}
$(#[$impl_m])*
unsafe impl<> ClassType for $for {
$(#[inherits($($inheritance_rest),+)])?
type Super = $superclass;
type Mutability = $mutability;
fn as_super(&self) -> &Self::Super {
&self.__superclass
}
fn as_super_mut(&mut self) -> &mut Self::Super {
&mut self.__superclass
}
$(const NAME: &'static str = $name_const;)?
}
);
$(#[$impl_m])*
const _: () = {
if $crate::__macro_helpers::size_of::<$name>() != 0 {
$crate::__macro_helpers::panic!($crate::__macro_helpers::concat!(
"the struct ",
$crate::__macro_helpers::stringify!($name),
" is not zero-sized!",
))
}
};
};
}
#[doc(hidden)]
#[macro_export]
macro_rules! __impl_as_ref_borrow {
{
impl ($($t:tt)*) for $for:ty {
fn as_ref($($self:tt)*) $ref:block
fn as_mut($($self_mut:tt)*) $mut:block
}
()
} => {};
{
impl ($($t:tt)*) for $for:ty {
fn as_ref($($self:tt)*) $ref:block
fn as_mut($($self_mut:tt)*) $mut:block
}
($item:ty, $($tail:ty,)*)
} => {
impl<$($t)*> $crate::__macro_helpers::AsRef<$item> for $for {
#[inline]
fn as_ref($($self)*) -> &$item $ref
}
impl<$($t)*> $crate::__macro_helpers::AsMut<$item> for $for {
#[inline]
fn as_mut($($self_mut)*) -> &mut $item $mut
}
// Borrow and BorrowMut are correct, since subclasses behaves
// identical to the class they inherit (message sending doesn't care).
//
// In particular, `Eq`, `Ord` and `Hash` all give the same results
// after borrow.
impl<$($t)*> $crate::__macro_helpers::Borrow<$item> for $for {
#[inline]
fn borrow($($self)*) -> &$item $ref
}
impl<$($t)*> $crate::__macro_helpers::BorrowMut<$item> for $for {
#[inline]
fn borrow_mut($($self_mut)*) -> &mut $item $mut
}
$crate::__impl_as_ref_borrow! {
impl ($($t)*) for $for {
fn as_ref($($self)*) $ref
fn as_mut($($self_mut)*) $mut
}
($($tail,)*)
}
};
// TODO: Expose a generic variant of the macro.
}
/// Note: While this is not public, it is still a breaking change to change
/// this, since framework crates rely on it.
#[doc(hidden)]
#[macro_export]
macro_rules! __inner_extern_class {
(
$(#[$m:meta])*
$v:vis struct $name:ident<$($t_struct:ident $(: $(?$b_sized_struct:ident)? $($b_struct:ident)? $(= $default:ty)?)?),* $(,)?> {
$superclass_field:ident: $superclass_field_ty:ty,
$($fields:tt)*
}
$(#[$impl_m:meta])*
unsafe impl<$($t_for:ident $(: $(?$b_sized_for:ident +)? $b_for:ident)?),* $(,)?> ClassType for $for:ty {
$(#[inherits($($inheritance_rest:ty),+ $(,)?)])?
type Super = $superclass:ty;
type Mutability = $mutability:ty;
fn as_super(&$as_super_self:ident) -> &Self::Super $as_super:block
fn as_super_mut(&mut $as_super_mut_self:ident) -> &mut Self::Super $as_super_mut:block
$(const NAME: &'static str = $name_const:expr;)?
}
) => {
$(#[$m])*
#[repr(C)]
$v struct $name<$($t_struct $(: $(?$b_sized_struct)? $($b_struct)? $(= $default)?)?),*> {
$superclass_field: $superclass_field_ty,
$($fields)*
}
$crate::__extern_class_impl_traits! {
$(#[$impl_m])*
unsafe impl ($($t_for $(: $(?$b_sized_for +)? $b_for)?),*) for $for {
INHERITS = [$superclass, $($($inheritance_rest,)+)? $crate::runtime::AnyObject];
fn as_super(&$as_super_self) $as_super
fn as_super_mut(&mut $as_super_mut_self) $as_super_mut
}
}
$(#[$impl_m])*
unsafe impl<$($t_for $(: $(?$b_sized_for +)? $b_for)?),*> ClassType for $for {
type Super = $superclass;
type Mutability = $mutability;
const NAME: &'static $crate::__macro_helpers::str = $crate::__select_name!($name; $($name_const)?);
#[inline]
fn class() -> &'static $crate::runtime::AnyClass {
$crate::__macro_helpers::assert_mutability_matches_superclass_mutability::<Self>();
$crate::__class_inner!(
$crate::__select_name!($name; $($name_const)?),
$crate::__hash_idents!($name)
)
}
#[inline]
fn as_super(&$as_super_self) -> &Self::Super $as_super
#[inline]
fn as_super_mut(&mut $as_super_mut_self) -> &mut Self::Super $as_super_mut
}
};
}
#[doc(hidden)]
#[macro_export]
macro_rules! __extern_class_impl_traits {
(
$(#[$impl_m:meta])*
unsafe impl ($($t:tt)*) for $for:ty {
INHERITS = [$superclass:ty $(, $inheritance_rest:ty)*];
fn as_super(&$as_super_self:ident) $as_super:block
fn as_super_mut(&mut $as_super_mut_self:ident) $as_super_mut:block
}
) => {
// SAFETY:
// - The item is FFI-safe with `#[repr(C)]`.
// - The encoding is taken from the inner item, and caller verifies
// that it actually inherits said object.
// - The rest of the struct's fields are ZSTs, so they don't influence
// the layout.
//
// Be aware that very rarely, this implementation is wrong because the
// class' instances do not have the encoding `Encoding::Object`.
//
// A known case is that `NSAutoreleasePool` has a different encoding.
// This should be fairly problem-free though, since that is still
// valid in Objective-C to represent that class' instances as
// `NSObject*`.
$(#[$impl_m])*
unsafe impl<$($t)*> $crate::RefEncode for $for {
const ENCODING_REF: $crate::Encoding
= <$superclass as $crate::RefEncode>::ENCODING_REF;
}
// SAFETY: This is a newtype wrapper over `AnyObject` (we even ensure
// that `AnyObject` is always last in our inheritance tree), so it is
// always safe to reinterpret as that.
//
// That the object must work with standard memory management is
// properly upheld by the fact that the superclass is required by
// `assert_mutability_matches_superclass_mutability` to implement
// `ClassType`, and hence must be a subclass of one of `NSObject`,
// `NSProxy` or some other class that ensures this (e.g. the object
// itself is not a root class).
$(#[$impl_m])*
unsafe impl<$($t)*> $crate::Message for $for {}
// SAFETY: An instance can always be _used_ in exactly the same way as
// its superclasses (though not necessarily _constructed_ in the same
// way, but `Deref` doesn't allow this).
//
// Remember; while we (the Rust side) may intentionally be forgetting
// which instance we're holding, the Objective-C side will remember,
// and will always dispatch to the correct method implementations.
//
// Any lifetime information that the object may have been holding is
// safely kept in the returned reference.
//
// Generics are discarded (for example in the case of `&NSArray<T>` to
// `&NSObject`), but if the generic contained a lifetime, that
// lifetime is still included in the returned reference, and is not
// erasable by e.g. `ClassType::retain` since `NSObject` does not
// allow that.
//
// Note that you can have two different variables pointing to the same
// object, `x: &T` and `y: &T::Target`, and this would be perfectly
// safe!
$(#[$impl_m])*
impl<$($t)*> $crate::__macro_helpers::Deref for $for {
type Target = $superclass;
#[inline]
fn deref(&$as_super_self) -> &Self::Target $as_super
}
// SAFETY: Mutability does not change anything in the above
// consideration, the lifetime of `&mut Self::Target` is still tied to
// `&mut self`.
//
// Usually we don't want to allow `&mut` of immutable objects like
// `NSString`, because their `NSCopying` implementation returns the
// same object, and would violate aliasing rules.
//
// But `&mut NSMutableString` -> `&mut NSString` safe, since the
// `NSCopying` implementation of `NSMutableString` is still used on
// the `&mut NSString`, and that is guaranteed to return a different
// object.
$(#[$impl_m])*
impl<$($t)*> $crate::__macro_helpers::DerefMut for $for {
#[inline]
fn deref_mut(&mut $as_super_mut_self) -> &mut Self::Target $as_super_mut
}
$(#[$impl_m])*
impl<$($t)*> $crate::__macro_helpers::AsRef<Self> for $for {
#[inline]
fn as_ref(&self) -> &Self {
self
}
}
$(#[$impl_m])*
impl<$($t)*> $crate::__macro_helpers::AsMut<Self> for $for {
#[inline]
fn as_mut(&mut self) -> &mut Self {
self
}
}
// Assume the meta attributes are all `cfg` attributes
$(#[$impl_m])*
$crate::__impl_as_ref_borrow! {
impl ($($t)*) for $for {
fn as_ref(&self) {
// Triggers Deref coercion depending on return type
&*self
}
fn as_mut(&mut self) {
// Triggers Deref coercion depending on return type
&mut *self
}
}
($superclass, $($inheritance_rest,)*)
}
};
}