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+use crate::imp::Box;
+use crate::{IUnknown, IUnknownImpl, Interface, InterfaceRef};
+use core::any::Any;
+use core::borrow::Borrow;
+use core::ops::Deref;
+use core::ptr::NonNull;
+
+/// Identifies types that can be placed in [`ComObject`].
+///
+/// This trait links types that can be placed in `ComObject` with the types generated by the
+/// `#[implement]` macro. The `#[implement]` macro generates implementations of this trait.
+/// The generated types contain the vtable layouts and refcount-related fields for the COM
+/// object implementation.
+///
+/// This trait is an implementation detail of the Windows crates.
+/// User code should not deal directly with this trait.
+///
+/// This trait is sort of the reverse of [`IUnknownImpl`]. This trait allows user code to use
+/// [`ComObject<T>`] instead of `ComObject<T_Impl>`.
+pub trait ComObjectInner: Sized {
+ /// The generated `<foo>_Impl` type (aka the "boxed" type or "outer" type).
+ type Outer: IUnknownImpl<Impl = Self>;
+
+ /// Moves an instance of this type into a new ComObject box and returns it.
+ ///
+ /// # Safety
+ ///
+ /// It is important that safe Rust code never be able to acquire an owned instance of a
+ /// generated "outer" COM object type, e.g. `<foo>_Impl`. This would be unsafe because the
+ /// `<foo>_Impl` object contains a reference count field and provides methods that adjust
+ /// the reference count, and destroy the object when the reference count reaches zero.
+ ///
+ /// Safe Rust code must only be able to interact with these values by accessing them via a
+ /// `ComObject` reference. `ComObject` handles adjusting reference counts and associates the
+ /// lifetime of a `&<foo>_Impl` with the lifetime of the related `ComObject`.
+ ///
+ /// The `#[implement]` macro generates the implementation of this `into_object` method.
+ /// The generated `into_object` method encapsulates the construction of the `<foo>_Impl`
+ /// object and immediately places it into the heap and returns a `ComObject` reference to it.
+ /// This ensures that our requirement -- that safe Rust code never own a `<foo>_Impl` value
+ /// directly -- is met.
+ fn into_object(self) -> ComObject<Self>;
+}
+
+/// Describes the COM interfaces implemented by a specific COM object.
+///
+/// The `#[implement]` macro generates implementations of this trait. Implementations are attached
+/// to the "outer" types generated by `#[implement]`, e.g. the `MyApp_Impl` type. Each
+/// implementation knows how to locate the interface-specific field within `MyApp_Impl`.
+///
+/// This trait is an implementation detail of the Windows crates.
+/// User code should not deal directly with this trait.
+pub trait ComObjectInterface<I: Interface> {
+ /// Gets a borrowed interface that is implemented by `T`.
+ fn as_interface_ref(&self) -> InterfaceRef<'_, I>;
+}
+
+/// A counted pointer to a type that implements COM interfaces, where the object has been
+/// placed in the heap (boxed).
+///
+/// This type exists so that you can place an object into the heap and query for COM interfaces,
+/// without losing the safe reference to the implementation object.
+///
+/// Because the pointer inside this type is known to be non-null, `Option<ComObject<T>>` should
+/// always have the same size as a single pointer.
+///
+/// # Safety
+///
+/// The contained `ptr` field is an owned, reference-counted pointer to a _pinned_ `Pin<Box<T::Outer>>`.
+/// Although this code does not currently use `Pin<T>`, it takes care not to expose any unsafe semantics
+/// to safe code. However, code that calls unsafe functions on [`ComObject`] must, like all unsafe code,
+/// understand and preserve invariants.
+#[repr(transparent)]
+pub struct ComObject<T: ComObjectInner> {
+ ptr: NonNull<T::Outer>,
+}
+
+impl<T: ComObjectInner> ComObject<T> {
+ /// Allocates a heap cell (box) and moves `value` into it. Returns a counted pointer to `value`.
+ pub fn new(value: T) -> Self {
+ T::into_object(value)
+ }
+
+ /// Creates a new `ComObject` that points to an existing boxed instance.
+ ///
+ /// # Safety
+ ///
+ /// The caller must ensure that `ptr` points to a valid, heap-allocated instance of `T::Outer`.
+ /// Normally, this pointer comes from using `Box::into_raw(Box::new(...))`.
+ ///
+ /// The pointed-to box must have a reference count that is greater than zero.
+ ///
+ /// This function takes ownership of the existing pointer; it does not call `AddRef`.
+ /// The reference count must accurately reflect all outstanding references to the box,
+ /// including `ptr` in the count.
+ pub unsafe fn from_raw(ptr: NonNull<T::Outer>) -> Self {
+ Self { ptr }
+ }
+
+ /// Gets a reference to the shared object stored in the box.
+ ///
+ /// [`ComObject`] also implements [`Deref`], so you can often deref directly into the object.
+ /// For those situations where using the [`Deref`] impl is inconvenient, you can use
+ /// this method to explicitly get a reference to the contents.
+ #[inline(always)]
+ pub fn get(&self) -> &T {
+ self.get_box().get_impl()
+ }
+
+ /// Gets a reference to the shared object's heap box.
+ #[inline(always)]
+ fn get_box(&self) -> &T::Outer {
+ unsafe { self.ptr.as_ref() }
+ }
+
+ // Note that we _do not_ provide a way to get a mutable reference to the outer box.
+ // It's ok to return `&mut T`, but not `&mut T::Outer`. That would allow someone to replace the
+ // contents of the entire object (box and reference count), which could lead to UB.
+ // This could maybe be solved by returning `Pin<&mut T::Outer>`, but that requires some
+ // additional thinking.
+
+ /// Gets a mutable reference to the object stored in the box, if the reference count
+ /// is exactly 1. If there are multiple references to this object then this returns `None`.
+ #[inline(always)]
+ pub fn get_mut(&mut self) -> Option<&mut T> {
+ if self.is_reference_count_one() {
+ // SAFETY: We must only return &mut T, *NOT* &mut T::Outer.
+ // Returning T::Outer would allow swapping the contents of the object, which would
+ // allow (incorrectly) modifying the reference count.
+ unsafe { Some(self.ptr.as_mut().get_impl_mut()) }
+ } else {
+ None
+ }
+ }
+
+ /// If this object has only a single object reference (i.e. this [`ComObject`] is the only
+ /// reference to the heap allocation), then this method will extract the inner `T`
+ /// (and return it in an `Ok`) and then free the heap allocation.
+ ///
+ /// If there is more than one reference to this object, then this returns `Err(self)`.
+ #[inline(always)]
+ pub fn take(self) -> Result<T, Self> {
+ if self.is_reference_count_one() {
+ let outer_box: Box<T::Outer> = unsafe { core::mem::transmute(self) };
+ Ok(outer_box.into_inner())
+ } else {
+ Err(self)
+ }
+ }
+
+ /// Casts to a given interface type.
+ ///
+ /// This always performs a `QueryInterface`, even if `T` is known to implement `I`.
+ /// If you know that `T` implements `I`, then use [`Self::as_interface`] or [`Self::to_interface`] because
+ /// those functions do not require a dynamic `QueryInterface` call.
+ #[inline(always)]
+ pub fn cast<I: Interface>(&self) -> windows_core::Result<I>
+ where
+ T::Outer: ComObjectInterface<IUnknown>,
+ {
+ let unknown = self.as_interface::<IUnknown>();
+ unknown.cast()
+ }
+
+ /// Gets a borrowed reference to an interface that is implemented by `T`.
+ ///
+ /// The returned reference does not have an additional reference count.
+ /// You can AddRef it by calling [`InterfaceRef::to_owned`].
+ #[inline(always)]
+ pub fn as_interface<I: Interface>(&self) -> InterfaceRef<'_, I>
+ where
+ T::Outer: ComObjectInterface<I>,
+ {
+ self.get_box().as_interface_ref()
+ }
+
+ /// Gets an owned (counted) reference to an interface that is implemented by this [`ComObject`].
+ #[inline(always)]
+ pub fn to_interface<I: Interface>(&self) -> I
+ where
+ T::Outer: ComObjectInterface<I>,
+ {
+ self.as_interface::<I>().to_owned()
+ }
+
+ /// Converts `self` into an interface that it implements.
+ ///
+ /// This does not need to adjust reference counts because `self` is consumed.
+ #[inline(always)]
+ pub fn into_interface<I: Interface>(self) -> I
+ where
+ T::Outer: ComObjectInterface<I>,
+ {
+ unsafe {
+ let raw = self.get_box().as_interface_ref().as_raw();
+ core::mem::forget(self);
+ I::from_raw(raw)
+ }
+ }
+
+ /// This casts the given COM interface to [`&dyn Any`]. It returns a reference to the "outer"
+ /// object, e.g. `MyApp_Impl`, not the inner `MyApp` object.
+ ///
+ /// `T` must be a type that has been annotated with `#[implement]`; this is checked at
+ /// compile-time by the generic constraints of this method. However, note that the
+ /// returned `&dyn Any` refers to the _outer_ implementation object that was generated by
+ /// `#[implement]`, i.e. the `MyApp_Impl` type, not the inner `MyApp` type.
+ ///
+ /// If the given object is not a Rust object, or is a Rust object but not `T`, or is a Rust
+ /// object that contains non-static lifetimes, then this function will return `Err(E_NOINTERFACE)`.
+ ///
+ /// The returned value is an owned (counted) reference; this function calls `AddRef` on the
+ /// underlying COM object. If you do not need an owned reference, then you can use the
+ /// [`Interface::cast_object_ref`] method instead, and avoid the cost of `AddRef` / `Release`.
+ pub fn cast_from<I>(interface: &I) -> crate::Result<Self>
+ where
+ I: Interface,
+ T::Outer: Any + 'static + IUnknownImpl<Impl = T>,
+ {
+ interface.cast_object()
+ }
+}
+
+impl<T: ComObjectInner + Default> Default for ComObject<T> {
+ fn default() -> Self {
+ Self::new(T::default())
+ }
+}
+
+impl<T: ComObjectInner> Drop for ComObject<T> {
+ fn drop(&mut self) {
+ unsafe {
+ T::Outer::Release(self.ptr.as_ptr());
+ }
+ }
+}
+
+impl<T: ComObjectInner> Clone for ComObject<T> {
+ #[inline(always)]
+ fn clone(&self) -> Self {
+ unsafe {
+ self.ptr.as_ref().AddRef();
+ Self { ptr: self.ptr }
+ }
+ }
+}
+
+impl<T: ComObjectInner> AsRef<T> for ComObject<T> {
+ #[inline(always)]
+ fn as_ref(&self) -> &T {
+ self.get()
+ }
+}
+
+impl<T: ComObjectInner> Deref for ComObject<T> {
+ type Target = T::Outer;
+
+ #[inline(always)]
+ fn deref(&self) -> &Self::Target {
+ self.get_box()
+ }
+}
+
+// There is no DerefMut implementation because we cannot statically guarantee
+// that the reference count is 1, which is a requirement for getting exclusive
+// access to the contents of the object. Use get_mut() for dynamically-checked
+// exclusive access.
+
+impl<T: ComObjectInner> From<T> for ComObject<T> {
+ fn from(value: T) -> ComObject<T> {
+ ComObject::new(value)
+ }
+}
+
+// Delegate hashing, if implemented.
+impl<T: ComObjectInner + core::hash::Hash> core::hash::Hash for ComObject<T> {
+ fn hash<H: core::hash::Hasher>(&self, state: &mut H) {
+ self.get().hash(state);
+ }
+}
+
+// If T is Send (or Sync) then the ComObject<T> is also Send (or Sync).
+// Since the actual object storage is in the heap, the object is never moved.
+unsafe impl<T: ComObjectInner + Send> Send for ComObject<T> {}
+unsafe impl<T: ComObjectInner + Sync> Sync for ComObject<T> {}
+
+impl<T: ComObjectInner + PartialEq> PartialEq for ComObject<T> {
+ fn eq(&self, other: &ComObject<T>) -> bool {
+ let inner_self: &T = self.get();
+ let other_self: &T = other.get();
+ inner_self == other_self
+ }
+}
+
+impl<T: ComObjectInner + Eq> Eq for ComObject<T> {}
+
+impl<T: ComObjectInner + PartialOrd> PartialOrd for ComObject<T> {
+ fn partial_cmp(&self, other: &Self) -> Option<core::cmp::Ordering> {
+ let inner_self: &T = self.get();
+ let other_self: &T = other.get();
+ <T as PartialOrd>::partial_cmp(inner_self, other_self)
+ }
+}
+
+impl<T: ComObjectInner + Ord> Ord for ComObject<T> {
+ fn cmp(&self, other: &Self) -> core::cmp::Ordering {
+ let inner_self: &T = self.get();
+ let other_self: &T = other.get();
+ <T as Ord>::cmp(inner_self, other_self)
+ }
+}
+
+impl<T: ComObjectInner + core::fmt::Debug> core::fmt::Debug for ComObject<T> {
+ fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+ <T as core::fmt::Debug>::fmt(self.get(), f)
+ }
+}
+
+impl<T: ComObjectInner + core::fmt::Display> core::fmt::Display for ComObject<T> {
+ fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+ <T as core::fmt::Display>::fmt(self.get(), f)
+ }
+}
+
+impl<T: ComObjectInner> Borrow<T> for ComObject<T> {
+ fn borrow(&self) -> &T {
+ self.get()
+ }
+}
+
+/// Enables applications to define COM objects using static storage. This is useful for factory
+/// objects, stateless objects, or objects which use need to contain or use mutable global state.
+///
+/// COM objects that are defined using `StaticComObject` have their storage placed directly in
+/// static storage; they are not stored in the heap.
+///
+/// COM objects defined using `StaticComObject` do have a reference count and this reference
+/// count is adjusted when owned COM interface references (e.g. `IFoo` and `IUnknown`) are created
+/// for the object. The reference count is initialized to 1.
+///
+/// # Example
+///
+/// ```rust,ignore
+/// #[implement(IFoo)]
+/// struct MyApp {
+/// // ...
+/// }
+///
+/// static MY_STATIC_APP: StaticComObject<MyApp> = MyApp { ... }.into_static();
+///
+/// fn get_my_static_ifoo() -> IFoo {
+/// MY_STATIC_APP.to_interface()
+/// }
+/// ```
+pub struct StaticComObject<T>
+where
+ T: ComObjectInner,
+{
+ outer: T::Outer,
+}
+
+// IMPORTANT: Do not expose any methods that return mutable access to the contents of StaticComObject.
+// Doing so would violate our safety invariants. For example, we provide a Deref impl but it would
+// be unsound to provide a DerefMut impl.
+impl<T> StaticComObject<T>
+where
+ T: ComObjectInner,
+{
+ /// Wraps `outer` in a `StaticComObject`.
+ pub const fn from_outer(outer: T::Outer) -> Self {
+ Self { outer }
+ }
+}
+
+impl<T> StaticComObject<T>
+where
+ T: ComObjectInner,
+{
+ /// Gets access to the contained value.
+ pub const fn get(&'static self) -> &'static T::Outer {
+ &self.outer
+ }
+}
+
+impl<T> core::ops::Deref for StaticComObject<T>
+where
+ T: ComObjectInner,
+{
+ type Target = T::Outer;
+
+ fn deref(&self) -> &Self::Target {
+ &self.outer
+ }
+}