Trait Transfer

pub trait Transfer: Sized + 'static {
    // Provided method
    fn type_name() -> &'static str { ... }
}

Allowing a type to be exposed to Lisp, where its values appear as opaque objects, or “embedded user pointers” (printed as #<user-ptr ...>).

When a (boxed) value of this type is transferred to Lisp, the GC becomes its owner. Afterwards, module code can only access it through immutable references.

The ’static bound disallows transferring short-lived references, which can become invalid while still being held by the Lisp runtime.

This works, because the returned string is copied into the Lisp runtime.

use emacs::{defun, Result};

#[defun]
fn foo(s: &String) -> Result<&str> {
    Ok(s)
}

This doesn’t work, because the function attempts to give the Lisp runtime a temporary reference.

use emacs::{defun, Result};

#[defun(user_ptr)]
fn foo(s: &String) -> Result<&str> {
    Ok(s)
}

Provided Methods

fn type_name() -> &'static str

Returns the name of this type. This is used to report runtime type errors, when a function expects values of this type, but receives values of a different type instead. The default implementation defers to the type_name function in std::any, which can be overridden for better error reporting.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementations on Foreign Types

impl<T: 'static> Transfer for Rc<T>

impl<T: 'static> Transfer for Arc<T>

impl<T: 'static> Transfer for RefCell<T>

impl<T: 'static> Transfer for Mutex<T>

impl<T: 'static> Transfer for RwLock<T>

Implementors