pyclass methods for Bound

Author: davidhewitt

src/instance.rs

@@ -1,4 +1,5 @@
 use crate::err::{self, PyDowncastError, PyErr, PyResult};
+use crate::ffi_ptr_ext::FfiPtrExt;
 use crate::pycell::{PyBorrowError, PyBorrowMutError, PyCell};
 use crate::pyclass::boolean_struct::{False, True};
 use crate::type_object::HasPyGilRef;
@@ -66,6 +67,43 @@ pub unsafe trait PyNativeType: Sized {
 #[repr(transparent)]
 pub struct Bound<'py, T>(Python<'py>, ManuallyDrop<Py<T>>);
 
+impl<'py, T> Bound<'py, T>
+where
+    T: PyClass,
+{
+    /// Creates a new instance `Bound<T>` of a `#[pyclass]` on the Python heap.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use pyo3::prelude::*;
+    ///
+    /// #[pyclass]
+    /// struct Foo {/* fields omitted */}
+    ///
+    /// # fn main() -> PyResult<()> {
+    /// Python::with_gil(|py| -> PyResult<Py<Foo>> {
+    ///     let foo: Bound<'_, Foo> = Bound::new(py, Foo {})?;
+    ///     Ok(foo.into())
+    /// })?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn new(
+        py: Python<'py>,
+        value: impl Into<PyClassInitializer<T>>,
+    ) -> PyResult<Bound<'py, T>> {
+        let initializer = value.into();
+        let obj = initializer.create_cell(py)?;
+        let ob = unsafe {
+            obj.cast::<ffi::PyObject>()
+                .assume_owned(py)
+                .downcast_into_unchecked()
+        };
+        Ok(ob)
+    }
+}
+
 impl<'py> Bound<'py, PyAny> {
     /// Constructs a new Bound from a pointer. Panics if ptr is null.
     ///
@@ -101,6 +139,149 @@ impl<'py> Bound<'py, PyAny> {
     }
 }
 
+impl<'py, T> Bound<'py, T>
+where
+    T: PyClass,
+{
+    /// Immutably borrows the value `T`.
+    ///
+    /// This borrow lasts while the returned [`PyRef`] exists.
+    /// Multiple immutable borrows can be taken out at the same time.
+    ///
+    /// For frozen classes, the simpler [`get`][Self::get] is available.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// # use pyo3::prelude::*;
+    /// #
+    /// #[pyclass]
+    /// struct Foo {
+    ///     inner: u8,
+    /// }
+    ///
+    /// # fn main() -> PyResult<()> {
+    /// Python::with_gil(|py| -> PyResult<()> {
+    ///     let foo: Bound<'_, Foo> = Bound::new(py, Foo { inner: 73 })?;
+    ///     let inner: &u8 = &foo.borrow().inner;
+    ///
+    ///     assert_eq!(*inner, 73);
+    ///     Ok(())
+    /// })?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// Panics if the value is currently mutably borrowed. For a non-panicking variant, use
+    /// [`try_borrow`](#method.try_borrow).
+    pub fn borrow(&'py self) -> PyRef<'py, T> {
+        self.get_cell().borrow()
+    }
+
+    /// Mutably borrows the value `T`.
+    ///
+    /// This borrow lasts while the returned [`PyRefMut`] exists.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use pyo3::prelude::*;
+    /// #
+    /// #[pyclass]
+    /// struct Foo {
+    ///     inner: u8,
+    /// }
+    ///
+    /// # fn main() -> PyResult<()> {
+    /// Python::with_gil(|py| -> PyResult<()> {
+    ///     let foo: Bound<'_, Foo> = Bound::new(py, Foo { inner: 73 })?;
+    ///     foo.borrow_mut().inner = 35;
+    ///
+    ///     assert_eq!(foo.borrow().inner, 35);
+    ///     Ok(())
+    /// })?;
+    /// # Ok(())
+    /// # }
+    ///  ```
+    ///
+    /// # Panics
+    /// Panics if the value is currently borrowed. For a non-panicking variant, use
+    /// [`try_borrow_mut`](#method.try_borrow_mut).
+    pub fn borrow_mut(&'py self) -> PyRefMut<'py, T>
+    where
+        T: PyClass<Frozen = False>,
+    {
+        self.get_cell().borrow_mut()
+    }
+
+    /// Attempts to immutably borrow the value `T`, returning an error if the value is currently mutably borrowed.
+    ///
+    /// The borrow lasts while the returned [`PyRef`] exists.
+    ///
+    /// This is the non-panicking variant of [`borrow`](#method.borrow).
+    ///
+    /// For frozen classes, the simpler [`get`][Self::get] is available.
+    pub fn try_borrow(&'py self) -> Result<PyRef<'py, T>, PyBorrowError> {
+        self.get_cell().try_borrow()
+    }
+
+    /// Attempts to mutably borrow the value `T`, returning an error if the value is currently borrowed.
+    ///
+    /// The borrow lasts while the returned [`PyRefMut`] exists.
+    ///
+    /// This is the non-panicking variant of [`borrow_mut`](#method.borrow_mut).
+    pub fn try_borrow_mut(&'py self) -> Result<PyRefMut<'py, T>, PyBorrowMutError>
+    where
+        T: PyClass<Frozen = False>,
+    {
+        self.get_cell().try_borrow_mut()
+    }
+
+    /// Provide an immutable borrow of the value `T` without acquiring the GIL.
+    ///
+    /// This is available if the class is [`frozen`][macro@crate::pyclass] and [`Sync`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::atomic::{AtomicUsize, Ordering};
+    /// # use pyo3::prelude::*;
+    ///
+    /// #[pyclass(frozen)]
+    /// struct FrozenCounter {
+    ///     value: AtomicUsize,
+    /// }
+    ///
+    /// Python::with_gil(|py| {
+    ///     let counter = FrozenCounter { value: AtomicUsize::new(0) };
+    ///
+    ///     let py_counter = Bound::new(py, counter).unwrap();
+    ///
+    ///     py_counter.get().value.fetch_add(1, Ordering::Relaxed);
+    /// });
+    /// ```
+    pub fn get(&self) -> &T
+    where
+        T: PyClass<Frozen = True> + Sync,
+    {
+        let cell = self.get_cell();
+        // SAFETY: The class itself is frozen and `Sync` and we do not access anything but `cell.contents.value`.
+        unsafe { &*cell.get_ptr() }
+    }
+
+    fn get_cell(&'py self) -> &'py PyCell<T> {
+        let cell = self.as_ptr().cast::<PyCell<T>>();
+        // SAFETY: Bound<T> is known to contain an object which is laid out in memory as a
+        // PyCell<T>.
+        //
+        // Strictly speaking for now `&'py PyCell<T>` is part of the "GIL Ref" API, so this
+        // could use some further refactoring later to avoid going through this reference.
+        unsafe { &*cell }
+    }
+}
+
 impl<'py, T> std::fmt::Debug for Bound<'py, T> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
         let any = self.as_any();