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use crate::{DynamicCast, MutPtr, MutRef, Ptr, Ref, StaticDowncast, StaticUpcast}; use std::ops::{Deref, DerefMut}; use std::{fmt, mem, ptr}; /// Objects that can be deleted using C++'s `delete` operator. /// /// This trait is automatically implemented for class types by `ritual`. pub trait CppDeletable: Sized { /// Calls C++'s `delete x` on `self`. /// /// # Safety /// /// The caller must make sure `self` contains a valid pointer. This function /// may invoke arbitrary foreign code, so no safety guarantees can be made. /// Note that deleting an object multiple times is undefined behavior. unsafe fn delete(&mut self); } /// An owning pointer to a C++ object. /// /// `CppBox` is automatically used in places where C++ class objects are passed by value /// and in return values of constructors because the ownership is apparent in these cases. /// However, sometimes an object is returned as a pointer but you must accept the ownership /// of the object. It's not possible to automatically determine ownership semantics /// of C++ code in this case, so you should manually convert `Ptr` to `CppBox` /// using `to_box` method. /// /// When `CppBox` is dropped, it will automatically delete the object using C++'s `delete` /// operator. /// /// Objects stored in `CppBox` are usually placed on the heap by the C++ code. /// /// If a C++ API accepts an object by pointer and takes ownership of it, it's not possible to /// automatically detect this, so you must manually convert `CppBox` to a non-owning `Ptr` /// using `into_ptr` before passing it to such a function. /// /// `&CppBox<T>` and `&mut CppBox<T>` implement operator traits and delegate them /// to the corresponding C++ operators. /// This means that you can use `&box1 + value` to access the object's `operator+`. /// /// `CppBox` implements `Deref` and `DerefMut`, allowing to call the object's methods /// directly. In addition, methods of the object's first base class are also directly available /// thanks to nested `Deref` implementations. /// /// If the object provides an iterator interface through `begin()` and `end()` functions, /// `&CppBox<T>` and `&mut CppBox<T>` will implement `IntoIterator`, /// so you can iterate on them directly. /// /// ### Safety /// /// It's not possible to automatically track the ownership of objects possibly managed by C++ /// libraries. The user must ensure that the object is alive while `CppBox` exists and that /// no pointers to the object are used after the object is deleted /// by `CppBox`'s `Drop` implementation. Note that with `CppBox`, /// it's possible to call unsafe C++ code without using any more unsafe code, for example, by /// using operator traits or simply dropping the box, so care should be taken when exposing /// `CppBox` in a safe interface. pub struct CppBox<T: CppDeletable>(ptr::NonNull<T>); impl<T: CppDeletable> CppBox<T> { /// Encapsulates the object into a `CppBox`. Returns `None` if the pointer is null. /// /// The same operation can be done by calling `to_box` function on `MutPtr`. /// /// You should use this function only for /// pointers that were created on C++ side and passed through /// a FFI boundary to Rust. An object created with C++ `new` /// must be deleted using C++ `delete`, which is executed by `CppBox`. /// /// Do not use this function for objects that would be deleted by other means. /// If another C++ object is the owner of the passed object, /// it will attempt to delete it. If `CppBox` containing the object still exists, /// it would result in a double deletion, which must never happen. /// /// Use `CppBox::into_ptr` to unwrap the pointer before passing it to /// a function that takes ownership of the object. /// /// ### Safety /// /// The pointer must point to an object that can be /// safely deleted using C++'s `delete` operator. /// The object must not be deleted by other means while `CppBox` exists. /// Any other pointers to the object must not be used after `CppBox` is dropped. pub unsafe fn new(ptr: MutPtr<T>) -> Option<Self> { Self::from_raw(ptr.as_mut_raw_ptr()) } /// Encapsulates the object into a `CppBox`. Returns `None` if the pointer is null. /// /// See `CppBox::new` for more information. /// /// ### Safety /// /// The pointer must point to an object that can be /// safely deleted using C++'s `delete` operator. /// The object must not be deleted by other means while `CppBox` exists. /// Any other pointers to the object must not be used after `CppBox` is dropped. pub unsafe fn from_raw(ptr: *mut T) -> Option<Self> { ptr::NonNull::new(ptr).map(CppBox) } } impl<T: CppDeletable> CppBox<T> { /// Returns a constant pointer to the value in the box. /// /// ### Safety /// /// This operation is safe as long as `self` is valid. pub unsafe fn as_ptr(&self) -> Ptr<T> { Ptr::from_raw(self.0.as_ptr()) } /// Returns a mutable pointer to the value in the box. /// /// ### Safety /// /// This operation is safe as long as `self` is valid. pub unsafe fn as_mut_ptr(&mut self) -> MutPtr<T> { MutPtr::from_raw(self.0.as_ptr()) } /// Returns a constant raw pointer to the value in the box. pub fn as_mut_raw_ptr(&mut self) -> *mut T { self.0.as_ptr() } /// Returns a mutable raw pointer to the value in the box. pub fn as_raw_ptr(&self) -> *const T { self.0.as_ptr() as *const T } /// Destroys the box without deleting the object and returns a raw pointer to the content. /// The caller of the function becomes the owner of the object and should /// ensure that the object will be deleted at some point. pub fn into_raw_ptr(self) -> *mut T { let ptr = self.0.as_ptr(); mem::forget(self); ptr } /// Destroys the box without deleting the object and returns a pointer to the content. /// The caller of the function becomes the owner of the object and should /// ensure that the object will be deleted at some point. /// /// ### Safety /// /// This operation is safe as long as `self` is valid. pub unsafe fn into_ptr(self) -> MutPtr<T> { let ptr = MutPtr::from_raw(self.0.as_ptr()); mem::forget(self); ptr } /// Returns a constant reference to the value in the box. /// /// ### Safety /// /// This operation is safe as long as `self` is valid. #[allow(clippy::should_implement_trait)] pub unsafe fn as_ref(&self) -> Ref<T> { Ref::from_raw_non_null(self.0) } /// Returns a mutable reference to the value in the box. /// /// ### Safety /// /// This operation is safe as long as `self` is valid. #[allow(clippy::should_implement_trait)] pub unsafe fn as_mut_ref(&mut self) -> MutRef<T> { MutRef::from_raw_non_null(self.0) } /// Returns a non-owning reference to the content converted to the base class type `U`. /// `CppBox` retains the ownership of the object. /// /// ### Safety /// /// This operation is safe as long as `self` is valid. pub unsafe fn static_upcast<U>(&self) -> Ref<U> where T: StaticUpcast<U>, { StaticUpcast::static_upcast(self.as_ptr()) .as_ref() .expect("StaticUpcast returned null on CppBox input") } /// Returns a non-owning reference to the content converted to the derived class type `U`. /// `CppBox` retains the ownership of the object. /// /// It's recommended to use `dynamic_cast` instead because it performs a checked conversion. /// /// ### Safety /// /// This operation is safe as long as `self` is valid and it's type is `U` or inherits from `U`. pub unsafe fn static_downcast<U>(&self) -> Ref<U> where T: StaticDowncast<U>, { StaticDowncast::static_downcast(self.as_ptr()) .as_ref() .expect("StaticDowncast returned null on CppBox input") } /// Returns a non-owning reference to the content converted to the derived class type `U`. /// `CppBox` retains the ownership of the object. Returns `None` if the object's type is not `U` /// and doesn't inherit `U`. /// /// ### Safety /// /// This operation is safe as long as `self` is valid. pub unsafe fn dynamic_cast<U>(&self) -> Option<Ref<U>> where T: DynamicCast<U>, { DynamicCast::dynamic_cast(self.as_ptr()).as_ref() } /// Returns a non-owning reference to the content converted to the base class type `U`. /// `CppBox` retains the ownership of the object. /// /// ### Safety /// /// This operation is safe as long as `self` is valid. pub unsafe fn static_upcast_mut<U>(&mut self) -> MutRef<U> where T: StaticUpcast<U>, { StaticUpcast::static_upcast_mut(self.as_mut_ptr()) .as_mut_ref() .expect("StaticUpcast returned null on CppBox input") } /// Returns a non-owning reference to the content converted to the derived class type `U`. /// `CppBox` retains the ownership of the object. /// /// It's recommended to use `dynamic_cast` instead because it performs a checked conversion. /// /// ### Safety /// /// This operation is safe as long as `self` is valid and it's type is `U` or inherits from `U`. pub unsafe fn static_downcast_mut<U>(&mut self) -> MutRef<U> where T: StaticDowncast<U>, { StaticDowncast::static_downcast_mut(self.as_mut_ptr()) .as_mut_ref() .expect("StaticDowncast returned null on CppBox input") } /// Returns a non-owning reference to the content converted to the derived class type `U`. /// `CppBox` retains the ownership of the object. Returns `None` if the object's type is not `U` /// and doesn't inherit `U`. /// /// ### Safety /// /// This operation is safe as long as `self` is valid. pub unsafe fn dynamic_cast_mut<U>(&mut self) -> Option<MutRef<U>> where T: DynamicCast<U>, { DynamicCast::dynamic_cast_mut(self.as_mut_ptr()).as_mut_ref() } } /// Allows to call member functions of `T` and its base classes directly on the pointer. impl<T: CppDeletable> Deref for CppBox<T> { type Target = T; fn deref(&self) -> &T { unsafe { self.0.as_ref() } } } /// Allows to call member functions of `T` and its base classes directly on the pointer. impl<T: CppDeletable> DerefMut for CppBox<T> { fn deref_mut(&mut self) -> &mut T { unsafe { self.0.as_mut() } } } /// Deletes the stored object using C++'s `delete` operator. impl<T: CppDeletable> Drop for CppBox<T> { fn drop(&mut self) { unsafe { T::delete(self.0.as_mut()); } } } impl<T: CppDeletable> fmt::Debug for CppBox<T> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { write!(f, "CppBox({:?})", self.0) } } #[cfg(test)] mod tests { use crate::{CppBox, CppDeletable, MutPtr}; use std::cell::RefCell; use std::rc::Rc; struct Struct1 { value: Rc<RefCell<i32>>, } unsafe extern "C" fn struct1_delete(this_ptr: *mut Struct1) { (*this_ptr).value.borrow_mut().clone_from(&42); } impl CppDeletable for Struct1 { unsafe fn delete(&mut self) { struct1_delete(self); } } #[test] fn test_drop_calls_deleter() { let value1 = Rc::new(RefCell::new(10)); let mut object1 = Struct1 { value: value1.clone(), }; assert!(*value1.borrow() == 10); unsafe { // TODO: remove all "as *mut _" because it's automatic CppBox::new(MutPtr::from_raw(&mut object1)); } assert!(*value1.borrow() == 42); } }