Trait PyCapsuleMethods

Source

pub trait PyCapsuleMethods<'py>: Sealed {
    // Required methods
    fn set_context(&self, context: *mut c_void) -> PyResult<()>;
    fn context(&self) -> PyResult<*mut c_void>;
    unsafe fn reference<T>(&self) -> &'py T;
    fn pointer(&self) -> *mut c_void;
    fn is_valid(&self) -> bool;
    fn name(&self) -> PyResult<Option<&'py CStr>>;
}

Expand description

Implementation of functionality for PyCapsule.

These methods are defined for the Bound<'py, PyCapsule> smart pointer, so to use method call syntax these methods are separated into a trait, because stable Rust does not yet support arbitrary_self_types.

Required Methods§

Source

fn set_context(&self, context: *mut c_void) -> PyResult<()>

Sets the context pointer in the capsule.

Returns an error if this capsule is not valid.

§Notes

The context is treated much like the value of the capsule, but should likely act as a place to store any state management when using the capsule.

If you want to store a Rust value as the context, and drop it from the destructor, use Box::into_raw to convert it into a pointer, see the example.

§Example

use std::os::raw::c_void;
use std::sync::mpsc::{channel, Sender};
use pyo3::{prelude::*, types::PyCapsule};

let (tx, rx) = channel::<String>();

fn destructor(val: u32, context: *mut c_void) {
    let ctx = unsafe { *Box::from_raw(context.cast::<Sender<String>>()) };
    ctx.send("Destructor called!".to_string()).unwrap();
}

Python::with_gil(|py| {
    let capsule =
        PyCapsule::new_with_destructor(py, 123, None, destructor as fn(u32, *mut c_void))
            .unwrap();
    let context = Box::new(tx);  // `Sender<String>` is our context, box it up and ship it!
    capsule.set_context(Box::into_raw(context).cast()).unwrap();
    // This scope will end, causing our destructor to be called...
});

assert_eq!(rx.recv(), Ok("Destructor called!".to_string()));