Struct I31

pub struct I31(/* private fields */);

Available on crate features gc and runtime only.

A 31-bit integer.

Represents WebAssembly’s (ref i31) and (ref null i31) (aka i31ref) references.

You can convert this into any of the (ref i31) supertypes such as (ref eq) or (ref any), and their nullable equivalents. After conversion, the resulting reference does not actually point at a GC object in the heap, instead it is a 31-bit integer that is stored unboxed/inline in the reference itself.

Example

// Enable the Wasm GC proposal for Wasm to use i31 references.
let mut config = Config::new();
config.wasm_gc(true);

let engine = Engine::new(&config)?;
let mut store = Store::new(&engine, ());

// A Wasm module that exports a function that increments an i31.
let module = Module::new(&engine, r#"
    (module
        (func (export "inc_i31") (param (ref i31)) (result (ref i31))
            local.get 0
            i31.get_u
            i32.const 1
            i32.add
            ref.i31
        )
"#)?;

// Instantiate the module.
let instance = Instance::new(&mut store, &module, &[])?;

// Get the exported `inc_i31` function.
let inc_i31 = instance.get_func(&mut store, "inc_i31").unwrap();

// Call the function using the untyped functions API, meaning we need to
// pack our `I31` argument into an `AnyRef` that is packed into a `Val`, and
// then we need to do the opposite unpacking to extract the result.
let i31 = I31::wrapping_u32(0x1234);
let anyref = AnyRef::from_i31(&mut store, i31);
let val = Val::AnyRef(Some(anyref));
let mut results = [Val::null_any_ref()];
inc_i31.call(&mut store, &[val], &mut results)?;
let nullable_anyref = results[0].unwrap_anyref();
let anyref = nullable_anyref.unwrap();
let i31 = anyref.unwrap_i31(&store)?;
assert_eq!(i31.get_u32(), 0x1235);

// Alternatively, we can use the typed function API to make this all a lot
// more ergonomic.
let inc_i31 = inc_i31.typed::<I31, I31>(&mut store)?;
let i31 = I31::wrapping_u32(0x5678);
let result = inc_i31.call(&mut store, i31)?;
assert_eq!(result.get_u32(), 0x5679);

Implementations

impl I31

pub fn new_u32(value: u32) -> Option<Self>

Construct a new I31 from the given unsigned value.

Returns None if the value does not fit in the bottom 31 bits.

Example

// This value does not fit into 31 bits.
assert!(I31::new_u32(0x8000_0000).is_none());

// This value does fit into 31 bits.
let x = I31::new_u32(5).unwrap();
assert_eq!(x.get_u32(), 5);

pub fn new_i32(value: i32) -> Option<Self>

Construct a new I31 from the given signed value.

Returns None if the value does not fit in the bottom 31 bits.

Example

// This value does not fit into 31 bits.
assert!(I31::new_i32(-2147483648).is_none());

// This value does fit into 31 bits.
let x = I31::new_i32(-5).unwrap();
assert_eq!(x.get_i32(), -5);

pub fn wrapping_u32(value: u32) -> Self

Construct a new I31 from the given unsigned value.

If the value doesn’t fit in the bottom 31 bits, it is wrapped such that the wrapped value does.

Example

// Values that fit in 31 bits are preserved.
let x = I31::wrapping_u32(5);
assert_eq!(x.get_u32(), 5);

// Values that do not fit in 31 bits are wrapped to 31 bits.
let y = I31::wrapping_u32(0xffff_ffff);
assert_eq!(y.get_u32(), 0x7fff_ffff);

pub fn wrapping_i32(value: i32) -> Self

Construct a new I31 from the given signed value.

If the value doesn’t fit in the bottom 31 bits, it is wrapped such that the wrapped value does.

Example

// Values that fit in 31 bits are preserved.
let x = I31::wrapping_i32(-5);
assert_eq!(x.get_i32(), -5);

// Values that do not fit in 31 bits are wrapped to 31 bits.
let y = I31::wrapping_i32(-1073741825); // 0xbfffffff
assert_eq!(y.get_i32(), 1073741823);    // 0x3fffffff

pub fn get_u32(&self) -> u32

Get this I31’s value as an unsigned integer.

Example

let x = I31::new_i32(-1).unwrap();
assert_eq!(x.get_u32(), 0x7fff_ffff);

pub fn get_i32(&self) -> i32

Get this I31’s value as a signed integer.

Example

let x = I31::new_u32(0x7fff_ffff).unwrap();
assert_eq!(x.get_i32(), -1);

Trait Implementations

impl Clone for I31

fn clone(&self) -> I31

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for I31

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

Formats the value using the given formatter.

impl Default for I31

fn default() -> I31

Returns the “default value” for a type.

impl Hash for I31

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for I31

fn eq(&self, other: &I31) -> 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 I31

impl Eq for I31

impl StructuralPartialEq for I31

impl WasmTy for I31