pyo3/
pycell.rs

1//! PyO3's interior mutability primitive.
2//!
3//! Rust has strict aliasing rules - you can either have any number of immutable (shared) references or one mutable
4//! reference. Python's ownership model is the complete opposite of that - any Python object
5//! can be referenced any number of times, and mutation is allowed from any reference.
6//!
7//! PyO3 deals with these differences by employing the [Interior Mutability]
8//! pattern. This requires that PyO3 enforces the borrowing rules and it has two mechanisms for
9//! doing so:
10//! - Statically it can enforce thread-safe access with the [`Python<'py>`](crate::Python) token.
11//!   All Rust code holding that token, or anything derived from it, can assume that they have
12//!   safe access to the Python interpreter's state. For this reason all the native Python objects
13//!   can be mutated through shared references.
14//! - However, methods and functions in Rust usually *do* need `&mut` references. While PyO3 can
15//!   use the [`Python<'py>`](crate::Python) token to guarantee thread-safe access to them, it cannot
16//!   statically guarantee uniqueness of `&mut` references. As such those references have to be tracked
17//!   dynamically at runtime, using `PyCell` and the other types defined in this module. This works
18//!   similar to std's [`RefCell`](std::cell::RefCell) type.
19//!
20//! # When *not* to use PyCell
21//!
22//! Usually you can use `&mut` references as method and function receivers and arguments, and you
23//! won't need to use `PyCell` directly:
24//!
25//! ```rust,no_run
26//! use pyo3::prelude::*;
27//!
28//! #[pyclass]
29//! struct Number {
30//!     inner: u32,
31//! }
32//!
33//! #[pymethods]
34//! impl Number {
35//!     fn increment(&mut self) {
36//!         self.inner += 1;
37//!     }
38//! }
39//! ```
40//!
41//! The [`#[pymethods]`](crate::pymethods) proc macro will generate this wrapper function (and more),
42//! using `PyCell` under the hood:
43//!
44//! ```rust,ignore
45//! # use pyo3::prelude::*;
46//! # #[pyclass]
47//! # struct Number {
48//! #    inner: u32,
49//! # }
50//! #
51//! # #[pymethods]
52//! # impl Number {
53//! #    fn increment(&mut self) {
54//! #        self.inner += 1;
55//! #    }
56//! # }
57//! #
58//! // The function which is exported to Python looks roughly like the following
59//! unsafe extern "C" fn __pymethod_increment__(
60//!     _slf: *mut pyo3::ffi::PyObject,
61//!     _args: *mut pyo3::ffi::PyObject,
62//! ) -> *mut pyo3::ffi::PyObject {
63//!     use :: pyo3 as _pyo3;
64//!     _pyo3::impl_::trampoline::noargs(_slf, _args, |py, _slf| {
65//! #       #[allow(deprecated)]
66//!         let _cell = py
67//!             .from_borrowed_ptr::<_pyo3::PyAny>(_slf)
68//!             .cast::<_pyo3::PyCell<Number>>()?;
69//!         let mut _ref = _cell.try_borrow_mut()?;
70//!         let _slf: &mut Number = &mut *_ref;
71//!         _pyo3::impl_::callback::convert(py, Number::increment(_slf))
72//!     })
73//! }
74//! ```
75//!
76//! # When to use PyCell
77//! ## Using pyclasses from Rust
78//!
79//! However, we *do* need `PyCell` if we want to call its methods from Rust:
80//! ```rust
81//! # use pyo3::prelude::*;
82//! #
83//! # #[pyclass]
84//! # struct Number {
85//! #     inner: u32,
86//! # }
87//! #
88//! # #[pymethods]
89//! # impl Number {
90//! #     fn increment(&mut self) {
91//! #         self.inner += 1;
92//! #     }
93//! # }
94//! # fn main() -> PyResult<()> {
95//! Python::attach(|py| {
96//!     let n = Py::new(py, Number { inner: 0 })?;
97//!
98//!     // We borrow the guard and then dereference
99//!     // it to get a mutable reference to Number
100//!     let mut guard: PyRefMut<'_, Number> = n.bind(py).borrow_mut();
101//!     let n_mutable: &mut Number = &mut *guard;
102//!
103//!     n_mutable.increment();
104//!
105//!     // To avoid panics we must dispose of the
106//!     // `PyRefMut` before borrowing again.
107//!     drop(guard);
108//!
109//!     let n_immutable: &Number = &n.bind(py).borrow();
110//!     assert_eq!(n_immutable.inner, 1);
111//!
112//!     Ok(())
113//! })
114//! # }
115//! ```
116//! ## Dealing with possibly overlapping mutable references
117//!
118//! It is also necessary to use `PyCell` if you can receive mutable arguments that may overlap.
119//! Suppose the following function that swaps the values of two `Number`s:
120//! ```
121//! # use pyo3::prelude::*;
122//! # #[pyclass]
123//! # pub struct Number {
124//! #     inner: u32,
125//! # }
126//! #[pyfunction]
127//! fn swap_numbers(a: &mut Number, b: &mut Number) {
128//!     std::mem::swap(&mut a.inner, &mut b.inner);
129//! }
130//! # fn main() {
131//! #     Python::attach(|py| {
132//! #         let n = Py::new(py, Number{inner: 35}).unwrap();
133//! #         let n2 = n.clone_ref(py);
134//! #         assert!(n.is(&n2));
135//! #         let fun = pyo3::wrap_pyfunction!(swap_numbers, py).unwrap();
136//! #         fun.call1((n, n2)).expect_err("Managed to create overlapping mutable references. Note: this is undefined behaviour.");
137//! #     });
138//! # }
139//! ```
140//! When users pass in the same `Number` as both arguments, one of the mutable borrows will
141//! fail and raise a `RuntimeError`:
142//! ```text
143//! >>> a = Number()
144//! >>> swap_numbers(a, a)
145//! Traceback (most recent call last):
146//!   File "<stdin>", line 1, in <module>
147//!   RuntimeError: Already borrowed
148//! ```
149//!
150//! It is better to write that function like this:
151//! ```rust,ignore
152//! # #![allow(deprecated)]
153//! # use pyo3::prelude::*;
154//! # #[pyclass]
155//! # pub struct Number {
156//! #     inner: u32,
157//! # }
158//! #[pyfunction]
159//! fn swap_numbers(a: &PyCell<Number>, b: &PyCell<Number>) {
160//!     // Check that the pointers are unequal
161//!     if !a.is(b) {
162//!         std::mem::swap(&mut a.borrow_mut().inner, &mut b.borrow_mut().inner);
163//!     } else {
164//!         // Do nothing - they are the same object, so don't need swapping.
165//!     }
166//! }
167//! # fn main() {
168//! #     // With duplicate numbers
169//! #     Python::attach(|py| {
170//! #         let n = Py::new(py, Number{inner: 35}).unwrap();
171//! #         let n2 = n.clone_ref(py);
172//! #         assert!(n.is(&n2));
173//! #         let fun = pyo3::wrap_pyfunction!(swap_numbers, py).unwrap();
174//! #         fun.call1((n, n2)).unwrap();
175//! #     });
176//! #
177//! #     // With two different numbers
178//! #     Python::attach(|py| {
179//! #         let n = Py::new(py, Number{inner: 35}).unwrap();
180//! #         let n2 = Py::new(py, Number{inner: 42}).unwrap();
181//! #         assert!(!n.is(&n2));
182//! #         let fun = pyo3::wrap_pyfunction!(swap_numbers, py).unwrap();
183//! #         fun.call1((&n, &n2)).unwrap();
184//! #         let n: u32 = n.borrow(py).inner;
185//! #         let n2: u32 = n2.borrow(py).inner;
186//! #         assert_eq!(n, 42);
187//! #         assert_eq!(n2, 35);
188//! #     });
189//! # }
190//! ```
191//! See the [guide] for more information.
192//!
193//! [guide]: https://pyo3.rs/latest/class.html#pycell-and-interior-mutability "PyCell and interior mutability"
194//! [Interior Mutability]: https://doc.rust-lang.org/book/ch15-05-interior-mutability.html "RefCell<T> and the Interior Mutability Pattern - The Rust Programming Language"
195
196use crate::conversion::IntoPyObject;
197use crate::exceptions::PyRuntimeError;
198use crate::ffi_ptr_ext::FfiPtrExt;
199use crate::internal_tricks::{ptr_from_mut, ptr_from_ref};
200use crate::pyclass::{boolean_struct::False, PyClass};
201use crate::{ffi, Borrowed, Bound, PyErr, Python};
202use std::convert::Infallible;
203use std::fmt;
204use std::mem::ManuallyDrop;
205use std::ops::{Deref, DerefMut};
206
207pub(crate) mod impl_;
208use impl_::{PyClassBorrowChecker, PyClassObjectLayout};
209
210/// A wrapper type for an immutably borrowed value from a [`Bound<'py, T>`].
211///
212/// See the [`Bound`] documentation for more information.
213///
214/// # Examples
215///
216/// You can use [`PyRef`] as an alternative to a `&self` receiver when
217/// - you need to access the pointer of the [`Bound`], or
218/// - you want to get a super class.
219/// ```
220/// # use pyo3::prelude::*;
221/// #[pyclass(subclass)]
222/// struct Parent {
223///     basename: &'static str,
224/// }
225///
226/// #[pyclass(extends=Parent)]
227/// struct Child {
228///     name: &'static str,
229///  }
230///
231/// #[pymethods]
232/// impl Child {
233///     #[new]
234///     fn new() -> (Self, Parent) {
235///         (Child { name: "Caterpillar" }, Parent { basename: "Butterfly" })
236///     }
237///
238///     fn format(slf: PyRef<'_, Self>) -> String {
239///         // We can get *mut ffi::PyObject from PyRef
240///         let refcnt = unsafe { pyo3::ffi::Py_REFCNT(slf.as_ptr()) };
241///         // We can get &Self::BaseType by as_ref
242///         let basename = slf.as_ref().basename;
243///         format!("{}(base: {}, cnt: {})", slf.name, basename, refcnt)
244///     }
245/// }
246/// # Python::attach(|py| {
247/// #     let sub = Py::new(py, Child::new()).unwrap();
248/// #     pyo3::py_run!(py, sub, "assert sub.format() == 'Caterpillar(base: Butterfly, cnt: 4)', sub.format()");
249/// # });
250/// ```
251///
252/// See the [module-level documentation](self) for more information.
253#[repr(transparent)]
254pub struct PyRef<'p, T: PyClass> {
255    // TODO: once the GIL Ref API is removed, consider adding a lifetime parameter to `PyRef` to
256    // store `Borrowed` here instead, avoiding reference counting overhead.
257    inner: Bound<'p, T>,
258}
259
260impl<'p, T: PyClass> PyRef<'p, T> {
261    /// Returns a `Python` token that is bound to the lifetime of the `PyRef`.
262    pub fn py(&self) -> Python<'p> {
263        self.inner.py()
264    }
265}
266
267impl<T, U> AsRef<U> for PyRef<'_, T>
268where
269    T: PyClass<BaseType = U>,
270    U: PyClass,
271{
272    fn as_ref(&self) -> &T::BaseType {
273        self.as_super()
274    }
275}
276
277impl<'py, T: PyClass> PyRef<'py, T> {
278    /// Returns the raw FFI pointer represented by self.
279    ///
280    /// # Safety
281    ///
282    /// Callers are responsible for ensuring that the pointer does not outlive self.
283    ///
284    /// The reference is borrowed; callers should not decrease the reference count
285    /// when they are finished with the pointer.
286    #[inline]
287    pub fn as_ptr(&self) -> *mut ffi::PyObject {
288        self.inner.as_ptr()
289    }
290
291    /// Returns an owned raw FFI pointer represented by self.
292    ///
293    /// # Safety
294    ///
295    /// The reference is owned; when finished the caller should either transfer ownership
296    /// of the pointer or decrease the reference count (e.g. with [`pyo3::ffi::Py_DecRef`](crate::ffi::Py_DecRef)).
297    #[inline]
298    pub fn into_ptr(self) -> *mut ffi::PyObject {
299        self.inner.clone().into_ptr()
300    }
301
302    #[track_caller]
303    pub(crate) fn borrow(obj: &Bound<'py, T>) -> Self {
304        Self::try_borrow(obj).expect("Already mutably borrowed")
305    }
306
307    pub(crate) fn try_borrow(obj: &Bound<'py, T>) -> Result<Self, PyBorrowError> {
308        let cell = obj.get_class_object();
309        cell.ensure_threadsafe();
310        cell.borrow_checker()
311            .try_borrow()
312            .map(|_| Self { inner: obj.clone() })
313    }
314}
315
316impl<'p, T, U> PyRef<'p, T>
317where
318    T: PyClass<BaseType = U>,
319    U: PyClass,
320{
321    /// Gets a `PyRef<T::BaseType>`.
322    ///
323    /// While `as_ref()` returns a reference of type `&T::BaseType`, this cannot be
324    /// used to get the base of `T::BaseType`.
325    ///
326    /// But with the help of this method, you can get hold of instances of the
327    /// super-superclass when needed.
328    ///
329    /// # Examples
330    /// ```
331    /// # use pyo3::prelude::*;
332    /// #[pyclass(subclass)]
333    /// struct Base1 {
334    ///     name1: &'static str,
335    /// }
336    ///
337    /// #[pyclass(extends=Base1, subclass)]
338    /// struct Base2 {
339    ///     name2: &'static str,
340    /// }
341    ///
342    /// #[pyclass(extends=Base2)]
343    /// struct Sub {
344    ///     name3: &'static str,
345    /// }
346    ///
347    /// #[pymethods]
348    /// impl Sub {
349    ///     #[new]
350    ///     fn new() -> PyClassInitializer<Self> {
351    ///         PyClassInitializer::from(Base1 { name1: "base1" })
352    ///             .add_subclass(Base2 { name2: "base2" })
353    ///             .add_subclass(Self { name3: "sub" })
354    ///     }
355    ///     fn name(slf: PyRef<'_, Self>) -> String {
356    ///         let subname = slf.name3;
357    ///         let super_ = slf.into_super();
358    ///         format!("{} {} {}", super_.as_ref().name1, super_.name2, subname)
359    ///     }
360    /// }
361    /// # Python::attach(|py| {
362    /// #     let sub = Py::new(py, Sub::new()).unwrap();
363    /// #     pyo3::py_run!(py, sub, "assert sub.name() == 'base1 base2 sub'")
364    /// # });
365    /// ```
366    pub fn into_super(self) -> PyRef<'p, U> {
367        let py = self.py();
368        let t_not_frozen = !<T::Frozen as crate::pyclass::boolean_struct::private::Boolean>::VALUE;
369        let u_frozen = <U::Frozen as crate::pyclass::boolean_struct::private::Boolean>::VALUE;
370        if t_not_frozen && u_frozen {
371            // If `T` is mutable subclass of `U` differ, then it is possible that we need to
372            // release the borrow count now. (e.g. `U` may have a noop borrow checker so
373            // dropping the `PyRef<U>` later would noop and leak the borrow we currently hold.)
374            //
375            // However it's nontrivial, if `U` itself has a mutable base class `V`,
376            // then the borrow checker of both `T` and `U` is the shared borrow checker of `V`.
377            //
378            // But it's really hard to prove that in the type system, the soundest thing we
379            // can do is just add a borrow to `U` now and then release the borrow of `T`.
380
381            self.inner
382                .as_super()
383                .get_class_object()
384                .borrow_checker()
385                .try_borrow()
386                .expect("this object is already borrowed");
387
388            self.inner
389                .get_class_object()
390                .borrow_checker()
391                .release_borrow()
392        };
393        PyRef {
394            inner: unsafe {
395                ManuallyDrop::new(self)
396                    .as_ptr()
397                    .assume_owned_unchecked(py)
398                    .cast_into_unchecked()
399            },
400        }
401    }
402
403    /// Borrows a shared reference to `PyRef<T::BaseType>`.
404    ///
405    /// With the help of this method, you can access attributes and call methods
406    /// on the superclass without consuming the `PyRef<T>`. This method can also
407    /// be chained to access the super-superclass (and so on).
408    ///
409    /// # Examples
410    /// ```
411    /// # use pyo3::prelude::*;
412    /// #[pyclass(subclass)]
413    /// struct Base {
414    ///     base_name: &'static str,
415    /// }
416    /// #[pymethods]
417    /// impl Base {
418    ///     fn base_name_len(&self) -> usize {
419    ///         self.base_name.len()
420    ///     }
421    /// }
422    ///
423    /// #[pyclass(extends=Base)]
424    /// struct Sub {
425    ///     sub_name: &'static str,
426    /// }
427    ///
428    /// #[pymethods]
429    /// impl Sub {
430    ///     #[new]
431    ///     fn new() -> (Self, Base) {
432    ///         (Self { sub_name: "sub_name" }, Base { base_name: "base_name" })
433    ///     }
434    ///     fn sub_name_len(&self) -> usize {
435    ///         self.sub_name.len()
436    ///     }
437    ///     fn format_name_lengths(slf: PyRef<'_, Self>) -> String {
438    ///         format!("{} {}", slf.as_super().base_name_len(), slf.sub_name_len())
439    ///     }
440    /// }
441    /// # Python::attach(|py| {
442    /// #     let sub = Py::new(py, Sub::new()).unwrap();
443    /// #     pyo3::py_run!(py, sub, "assert sub.format_name_lengths() == '9 8'")
444    /// # });
445    /// ```
446    pub fn as_super(&self) -> &PyRef<'p, U> {
447        let ptr = ptr_from_ref::<Bound<'p, T>>(&self.inner)
448            // `Bound<T>` has the same layout as `Bound<T::BaseType>`
449            .cast::<Bound<'p, T::BaseType>>()
450            // `Bound<T::BaseType>` has the same layout as `PyRef<T::BaseType>`
451            .cast::<PyRef<'p, T::BaseType>>();
452        unsafe { &*ptr }
453    }
454}
455
456impl<T: PyClass> Deref for PyRef<'_, T> {
457    type Target = T;
458
459    #[inline]
460    fn deref(&self) -> &T {
461        unsafe { &*self.inner.get_class_object().get_ptr() }
462    }
463}
464
465impl<T: PyClass> Drop for PyRef<'_, T> {
466    fn drop(&mut self) {
467        self.inner
468            .get_class_object()
469            .borrow_checker()
470            .release_borrow()
471    }
472}
473
474impl<'py, T: PyClass> IntoPyObject<'py> for PyRef<'py, T> {
475    type Target = T;
476    type Output = Bound<'py, T>;
477    type Error = Infallible;
478
479    #[cfg(feature = "experimental-inspect")]
480    const OUTPUT_TYPE: &'static str = T::PYTHON_TYPE;
481
482    fn into_pyobject(self, _py: Python<'py>) -> Result<Self::Output, Self::Error> {
483        Ok(self.inner.clone())
484    }
485}
486
487impl<'a, 'py, T: PyClass> IntoPyObject<'py> for &'a PyRef<'py, T> {
488    type Target = T;
489    type Output = Borrowed<'a, 'py, T>;
490    type Error = Infallible;
491
492    #[cfg(feature = "experimental-inspect")]
493    const OUTPUT_TYPE: &'static str = T::PYTHON_TYPE;
494
495    fn into_pyobject(self, _py: Python<'py>) -> Result<Self::Output, Self::Error> {
496        Ok(self.inner.as_borrowed())
497    }
498}
499
500impl<T: PyClass + fmt::Debug> fmt::Debug for PyRef<'_, T> {
501    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
502        fmt::Debug::fmt(&**self, f)
503    }
504}
505
506/// A wrapper type for a mutably borrowed value from a [`Bound<'py, T>`].
507///
508/// See the [module-level documentation](self) for more information.
509#[repr(transparent)]
510pub struct PyRefMut<'p, T: PyClass<Frozen = False>> {
511    // TODO: once the GIL Ref API is removed, consider adding a lifetime parameter to `PyRef` to
512    // store `Borrowed` here instead, avoiding reference counting overhead.
513    inner: Bound<'p, T>,
514}
515
516impl<'p, T: PyClass<Frozen = False>> PyRefMut<'p, T> {
517    /// Returns a `Python` token that is bound to the lifetime of the `PyRefMut`.
518    pub fn py(&self) -> Python<'p> {
519        self.inner.py()
520    }
521}
522
523impl<T, U> AsRef<U> for PyRefMut<'_, T>
524where
525    T: PyClass<BaseType = U, Frozen = False>,
526    U: PyClass<Frozen = False>,
527{
528    fn as_ref(&self) -> &T::BaseType {
529        PyRefMut::downgrade(self).as_super()
530    }
531}
532
533impl<T, U> AsMut<U> for PyRefMut<'_, T>
534where
535    T: PyClass<BaseType = U, Frozen = False>,
536    U: PyClass<Frozen = False>,
537{
538    fn as_mut(&mut self) -> &mut T::BaseType {
539        self.as_super()
540    }
541}
542
543impl<'py, T: PyClass<Frozen = False>> PyRefMut<'py, T> {
544    /// Returns the raw FFI pointer represented by self.
545    ///
546    /// # Safety
547    ///
548    /// Callers are responsible for ensuring that the pointer does not outlive self.
549    ///
550    /// The reference is borrowed; callers should not decrease the reference count
551    /// when they are finished with the pointer.
552    #[inline]
553    pub fn as_ptr(&self) -> *mut ffi::PyObject {
554        self.inner.as_ptr()
555    }
556
557    /// Returns an owned raw FFI pointer represented by self.
558    ///
559    /// # Safety
560    ///
561    /// The reference is owned; when finished the caller should either transfer ownership
562    /// of the pointer or decrease the reference count (e.g. with [`pyo3::ffi::Py_DecRef`](crate::ffi::Py_DecRef)).
563    #[inline]
564    pub fn into_ptr(self) -> *mut ffi::PyObject {
565        self.inner.clone().into_ptr()
566    }
567
568    #[inline]
569    #[track_caller]
570    pub(crate) fn borrow(obj: &Bound<'py, T>) -> Self {
571        Self::try_borrow(obj).expect("Already borrowed")
572    }
573
574    pub(crate) fn try_borrow(obj: &Bound<'py, T>) -> Result<Self, PyBorrowMutError> {
575        let cell = obj.get_class_object();
576        cell.ensure_threadsafe();
577        cell.borrow_checker()
578            .try_borrow_mut()
579            .map(|_| Self { inner: obj.clone() })
580    }
581
582    pub(crate) fn downgrade(slf: &Self) -> &PyRef<'py, T> {
583        // `PyRefMut<T>` and `PyRef<T>` have the same layout
584        unsafe { &*ptr_from_ref(slf).cast() }
585    }
586}
587
588impl<'p, T, U> PyRefMut<'p, T>
589where
590    T: PyClass<BaseType = U, Frozen = False>,
591    U: PyClass<Frozen = False>,
592{
593    /// Gets a `PyRef<T::BaseType>`.
594    ///
595    /// See [`PyRef::into_super`] for more.
596    pub fn into_super(self) -> PyRefMut<'p, U> {
597        let py = self.py();
598        PyRefMut {
599            inner: unsafe {
600                ManuallyDrop::new(self)
601                    .as_ptr()
602                    .assume_owned_unchecked(py)
603                    .cast_into_unchecked()
604            },
605        }
606    }
607
608    /// Borrows a mutable reference to `PyRefMut<T::BaseType>`.
609    ///
610    /// With the help of this method, you can mutate attributes and call mutating
611    /// methods on the superclass without consuming the `PyRefMut<T>`. This method
612    /// can also be chained to access the super-superclass (and so on).
613    ///
614    /// See [`PyRef::as_super`] for more.
615    pub fn as_super(&mut self) -> &mut PyRefMut<'p, U> {
616        let ptr = ptr_from_mut::<Bound<'p, T>>(&mut self.inner)
617            // `Bound<T>` has the same layout as `Bound<T::BaseType>`
618            .cast::<Bound<'p, T::BaseType>>()
619            // `Bound<T::BaseType>` has the same layout as `PyRefMut<T::BaseType>`,
620            // and the mutable borrow on `self` prevents aliasing
621            .cast::<PyRefMut<'p, T::BaseType>>();
622        unsafe { &mut *ptr }
623    }
624}
625
626impl<T: PyClass<Frozen = False>> Deref for PyRefMut<'_, T> {
627    type Target = T;
628
629    #[inline]
630    fn deref(&self) -> &T {
631        unsafe { &*self.inner.get_class_object().get_ptr() }
632    }
633}
634
635impl<T: PyClass<Frozen = False>> DerefMut for PyRefMut<'_, T> {
636    #[inline]
637    fn deref_mut(&mut self) -> &mut T {
638        unsafe { &mut *self.inner.get_class_object().get_ptr() }
639    }
640}
641
642impl<T: PyClass<Frozen = False>> Drop for PyRefMut<'_, T> {
643    fn drop(&mut self) {
644        self.inner
645            .get_class_object()
646            .borrow_checker()
647            .release_borrow_mut()
648    }
649}
650
651impl<'py, T: PyClass<Frozen = False>> IntoPyObject<'py> for PyRefMut<'py, T> {
652    type Target = T;
653    type Output = Bound<'py, T>;
654    type Error = Infallible;
655
656    #[cfg(feature = "experimental-inspect")]
657    const OUTPUT_TYPE: &'static str = T::PYTHON_TYPE;
658
659    fn into_pyobject(self, _py: Python<'py>) -> Result<Self::Output, Self::Error> {
660        Ok(self.inner.clone())
661    }
662}
663
664impl<'a, 'py, T: PyClass<Frozen = False>> IntoPyObject<'py> for &'a PyRefMut<'py, T> {
665    type Target = T;
666    type Output = Borrowed<'a, 'py, T>;
667    type Error = Infallible;
668
669    #[cfg(feature = "experimental-inspect")]
670    const OUTPUT_TYPE: &'static str = T::PYTHON_TYPE;
671
672    fn into_pyobject(self, _py: Python<'py>) -> Result<Self::Output, Self::Error> {
673        Ok(self.inner.as_borrowed())
674    }
675}
676
677impl<T: PyClass<Frozen = False> + fmt::Debug> fmt::Debug for PyRefMut<'_, T> {
678    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
679        fmt::Debug::fmt(self.deref(), f)
680    }
681}
682
683/// An error type returned by [`Bound::try_borrow`].
684///
685/// If this error is allowed to bubble up into Python code it will raise a `RuntimeError`.
686pub struct PyBorrowError {
687    _private: (),
688}
689
690impl fmt::Debug for PyBorrowError {
691    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
692        f.debug_struct("PyBorrowError").finish()
693    }
694}
695
696impl fmt::Display for PyBorrowError {
697    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
698        fmt::Display::fmt("Already mutably borrowed", f)
699    }
700}
701
702impl From<PyBorrowError> for PyErr {
703    fn from(other: PyBorrowError) -> Self {
704        PyRuntimeError::new_err(other.to_string())
705    }
706}
707
708/// An error type returned by [`Bound::try_borrow_mut`].
709///
710/// If this error is allowed to bubble up into Python code it will raise a `RuntimeError`.
711pub struct PyBorrowMutError {
712    _private: (),
713}
714
715impl fmt::Debug for PyBorrowMutError {
716    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
717        f.debug_struct("PyBorrowMutError").finish()
718    }
719}
720
721impl fmt::Display for PyBorrowMutError {
722    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
723        fmt::Display::fmt("Already borrowed", f)
724    }
725}
726
727impl From<PyBorrowMutError> for PyErr {
728    fn from(other: PyBorrowMutError) -> Self {
729        PyRuntimeError::new_err(other.to_string())
730    }
731}
732
733#[cfg(test)]
734#[cfg(feature = "macros")]
735mod tests {
736
737    use super::*;
738
739    #[crate::pyclass]
740    #[pyo3(crate = "crate")]
741    #[derive(Copy, Clone, PartialEq, Eq, Debug)]
742    struct SomeClass(i32);
743
744    #[test]
745    fn test_as_ptr() {
746        Python::attach(|py| {
747            let cell = Bound::new(py, SomeClass(0)).unwrap();
748            let ptr = cell.as_ptr();
749
750            assert_eq!(cell.borrow().as_ptr(), ptr);
751            assert_eq!(cell.borrow_mut().as_ptr(), ptr);
752        })
753    }
754
755    #[test]
756    fn test_into_ptr() {
757        Python::attach(|py| {
758            let cell = Bound::new(py, SomeClass(0)).unwrap();
759            let ptr = cell.as_ptr();
760
761            assert_eq!(cell.borrow().into_ptr(), ptr);
762            unsafe { ffi::Py_DECREF(ptr) };
763
764            assert_eq!(cell.borrow_mut().into_ptr(), ptr);
765            unsafe { ffi::Py_DECREF(ptr) };
766        })
767    }
768
769    #[crate::pyclass]
770    #[pyo3(crate = "crate", subclass)]
771    struct BaseClass {
772        val1: usize,
773    }
774
775    #[crate::pyclass]
776    #[pyo3(crate = "crate", extends=BaseClass, subclass)]
777    struct SubClass {
778        val2: usize,
779    }
780
781    #[crate::pyclass]
782    #[pyo3(crate = "crate", extends=SubClass)]
783    struct SubSubClass {
784        val3: usize,
785    }
786
787    #[crate::pymethods]
788    #[pyo3(crate = "crate")]
789    impl SubSubClass {
790        #[new]
791        fn new(py: Python<'_>) -> crate::Py<SubSubClass> {
792            let init = crate::PyClassInitializer::from(BaseClass { val1: 10 })
793                .add_subclass(SubClass { val2: 15 })
794                .add_subclass(SubSubClass { val3: 20 });
795            crate::Py::new(py, init).expect("allocation error")
796        }
797
798        fn get_values(self_: PyRef<'_, Self>) -> (usize, usize, usize) {
799            let val1 = self_.as_super().as_super().val1;
800            let val2 = self_.as_super().val2;
801            (val1, val2, self_.val3)
802        }
803
804        fn double_values(mut self_: PyRefMut<'_, Self>) {
805            self_.as_super().as_super().val1 *= 2;
806            self_.as_super().val2 *= 2;
807            self_.val3 *= 2;
808        }
809    }
810
811    #[test]
812    fn test_pyref_as_super() {
813        Python::attach(|py| {
814            let obj = SubSubClass::new(py).into_bound(py);
815            let pyref = obj.borrow();
816            assert_eq!(pyref.as_super().as_super().val1, 10);
817            assert_eq!(pyref.as_super().val2, 15);
818            assert_eq!(pyref.as_ref().val2, 15); // `as_ref` also works
819            assert_eq!(pyref.val3, 20);
820            assert_eq!(SubSubClass::get_values(pyref), (10, 15, 20));
821        });
822    }
823
824    #[test]
825    fn test_pyrefmut_as_super() {
826        Python::attach(|py| {
827            let obj = SubSubClass::new(py).into_bound(py);
828            assert_eq!(SubSubClass::get_values(obj.borrow()), (10, 15, 20));
829            {
830                let mut pyrefmut = obj.borrow_mut();
831                assert_eq!(pyrefmut.as_super().as_ref().val1, 10);
832                pyrefmut.as_super().as_super().val1 -= 5;
833                pyrefmut.as_super().val2 -= 3;
834                pyrefmut.as_mut().val2 -= 2; // `as_mut` also works
835                pyrefmut.val3 -= 5;
836            }
837            assert_eq!(SubSubClass::get_values(obj.borrow()), (5, 10, 15));
838            SubSubClass::double_values(obj.borrow_mut());
839            assert_eq!(SubSubClass::get_values(obj.borrow()), (10, 20, 30));
840        });
841    }
842
843    #[test]
844    fn test_pyrefs_in_python() {
845        Python::attach(|py| {
846            let obj = SubSubClass::new(py);
847            crate::py_run!(py, obj, "assert obj.get_values() == (10, 15, 20)");
848            crate::py_run!(py, obj, "assert obj.double_values() is None");
849            crate::py_run!(py, obj, "assert obj.get_values() == (20, 30, 40)");
850        });
851    }
852
853    #[test]
854    fn test_into_frozen_super_released_borrow() {
855        #[crate::pyclass]
856        #[pyo3(crate = "crate", subclass, frozen)]
857        struct BaseClass {}
858
859        #[crate::pyclass]
860        #[pyo3(crate = "crate", extends=BaseClass, subclass)]
861        struct SubClass {}
862
863        #[crate::pymethods]
864        #[pyo3(crate = "crate")]
865        impl SubClass {
866            #[new]
867            fn new(py: Python<'_>) -> Bound<'_, SubClass> {
868                let init = crate::PyClassInitializer::from(BaseClass {}).add_subclass(SubClass {});
869                Bound::new(py, init).expect("allocation error")
870            }
871        }
872
873        Python::attach(|py| {
874            let obj = SubClass::new(py);
875            drop(obj.borrow().into_super());
876            assert!(obj.try_borrow_mut().is_ok());
877        })
878    }
879
880    #[test]
881    fn test_into_frozen_super_mutable_base_holds_borrow() {
882        #[crate::pyclass]
883        #[pyo3(crate = "crate", subclass)]
884        struct BaseClass {}
885
886        #[crate::pyclass]
887        #[pyo3(crate = "crate", extends=BaseClass, subclass, frozen)]
888        struct SubClass {}
889
890        #[crate::pyclass]
891        #[pyo3(crate = "crate", extends=SubClass, subclass)]
892        struct SubSubClass {}
893
894        #[crate::pymethods]
895        #[pyo3(crate = "crate")]
896        impl SubSubClass {
897            #[new]
898            fn new(py: Python<'_>) -> Bound<'_, SubSubClass> {
899                let init = crate::PyClassInitializer::from(BaseClass {})
900                    .add_subclass(SubClass {})
901                    .add_subclass(SubSubClass {});
902                Bound::new(py, init).expect("allocation error")
903            }
904        }
905
906        Python::attach(|py| {
907            let obj = SubSubClass::new(py);
908            let _super_borrow = obj.borrow().into_super();
909            // the whole object still has an immutable borrow, so we cannot
910            // borrow any part mutably (the borrowflag is shared)
911            assert!(obj.try_borrow_mut().is_err());
912        })
913    }
914}