Struct NoExtern

pub struct NoExtern { /* private fields */ }

A reference to the abstract noextern heap value.

The are no instances of (ref noextern): it is an uninhabited type.

There is precisely one instance of (ref null noextern), aka nullexternref: the null reference.

This NoExtern Rust type’s sole purpose is for use with Func::wrap- and Func::typed-style APIs for statically typing a function as taking or returning a (ref null noextern) (aka Option<NoExtern>) which is always None.

Example

let mut config = Config::new();
config.wasm_function_references(true);
config.wasm_gc(true);
let engine = Engine::new(&config)?;

let module = Module::new(
    &engine,
    r#"
        (module
            (func (export "f") (param (ref null noextern))
                ;; If the reference is null, return.
                local.get 0
                ref.is_null noextern
                br_if 0

                ;; If the reference was not null (which is impossible)
                ;; then raise a trap.
                unreachable
            )
        )
    "#,
)?;

let mut store = Store::new(&engine, ());
let instance = Instance::new(&mut store, &module, &[])?;
let f = instance.get_func(&mut store, "f").unwrap();

// We can cast a `(ref null noextern)`-taking function into a typed function that
// takes an `Option<NoExtern>` via the `Func::typed` method.
let f = f.typed::<Option<NoExtern>, ()>(&store)?;

// We can call the typed function, passing the null `noextern` reference.
let result = f.call(&mut store, NoExtern::null());

// The function should not have trapped, because the reference we gave it was
// null (as it had to be, since `NoExtern` is uninhabited).
assert!(result.is_ok());

Implementations

impl NoExtern

pub fn null() -> Option<NoExtern>

Get the null (ref null noextern) (aka nullexternref) reference.

pub fn null_ref() -> Ref

Get the null (ref null noextern) (aka nullexternref) reference as a Ref.

pub fn null_val() -> Val

Get the null (ref null noextern) (aka nullexternref) reference as a Val.

Trait Implementations

impl Clone for NoExtern

fn clone(&self) -> NoExtern

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for NoExtern

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl PartialEq for NoExtern

fn eq(&self, other: &NoExtern) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for NoExtern

impl Eq for NoExtern

impl StructuralPartialEq for NoExtern

impl WasmTy for NoExtern