Struct cffi::BoxMarshaler

pub struct BoxMarshaler<T: ?Sized>(_);

The Box marshaler is the catch-all just-throw-it-on-the-heap opaque pointer solution.

It supports the following modes of operation:

To the foreign interface:

• T → *const/mut T
• Box<T> → *const/*mut T

From the foreign interface:

• *const/mut T → Box<T> (owned)
• *const T → &T (ref)
• *mut T → &mut T (mut ref)

Freeing T

Your foreign code should ensure that they call BoxMarshaler::<*mut/const T, Box<T>>::from_foreign, which will allow you to consume the boxed T and allow it to drop as per Rust’s usual rules.

Example

use cffi::{BoxMarshaler, FromForeign, ToForeign};

struct Something {
    data: Vec<u8>
}

fn demo() {
    let something = Something { data: vec![1, 3, 55] };

    // BoxMarshaler::to_foreign is Infallible
    let ptr: *const Something = BoxMarshaler::to_foreign(something).unwrap();

    /* send `ptr` over ffi, process it in some way, etc */

    // This isn't infallible though, checks for null pointers.
    let boxed: Box<Something> = match BoxMarshaler::from_foreign(ptr) {
        Ok(v) => v,
        Err(e) => panic!("!")
    };

    // Let the boxed item drop and it is freed. :)
}

Trait Implementations

impl<T> FromForeign<*const T, Box<T, Global>> for BoxMarshaler<T>

type Error = Box<dyn Error>

unsafe fn from_foreign(foreign: *const T) -> Result<Box<T>, Self::Error>

impl<T> InputType for BoxMarshaler<T>

type Foreign = *const T

type ForeignTraitObject = ()

impl<T> ReturnType for BoxMarshaler<T>

type Foreign = *const T

type ForeignTraitObject = ()

fn foreign_default() -> Self::Foreign

fn foreign_default_trait_object() -> Self::ForeignTraitObject

impl<T> ToForeign<Box<T, Global>, *const T> for BoxMarshaler<T>

type Error = Infallible

fn to_foreign(local: Box<T>) -> Result<*const T, Self::Error>

impl<T: ?Sized> ToForeign<Result<Box<T, Global>, Box<dyn Error + 'static, Global>>, *const T> for BoxMarshaler<T>

type Error = Box<dyn Error>

fn to_foreign(
    local: Result<Box<T>, Box<dyn Error>>
) -> Result<*const T, Self::Error>