Struct wasmtime::Global

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

A WebAssembly global value which can be read and written to.

A global in WebAssembly is sort of like a global variable within an Instance. The global.get and global.set instructions will modify and read global values in a wasm module. Globals can either be imported or exported from wasm modules.

A Global “belongs” to the store that it was originally created within (either via Global::new or via instantiating a Module). Operations on a Global only work with the store it belongs to, and if another store is passed in by accident then methods will panic.

Implementations

impl Global

pub fn new(store: impl AsContextMut, ty: GlobalType, val: Val) -> Result<Global>

Creates a new WebAssembly global value with the provide type ty and initial value val.

The store argument will be the owner of the Global returned. Using the returned Global other items in the store may access this global. For example this could be provided as an argument to Instance::new or Linker::define.

Errors

Returns an error if the ty provided does not match the type of the value val, or if val comes from a different store than store.

Examples

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

let ty = GlobalType::new(ValType::I32, Mutability::Const);
let i32_const = Global::new(&mut store, ty, 1i32.into())?;
let ty = GlobalType::new(ValType::F64, Mutability::Var);
let f64_mut = Global::new(&mut store, ty, 2.0f64.into())?;

let module = Module::new(
    &engine,
    "(module
        (global (import \"\" \"i32-const\") i32)
        (global (import \"\" \"f64-mut\") (mut f64))
    )"
)?;

let mut linker = Linker::new(&engine);
linker.define(&store, "", "i32-const", i32_const)?;
linker.define(&store, "", "f64-mut", f64_mut)?;

let instance = linker.instantiate(&mut store, &module)?;
// ...

pub fn ty(&self, store: impl AsContext) -> GlobalType

Returns the underlying type of this global.

Panics

Panics if store does not own this global.

pub fn get(&self, store: impl AsContextMut) -> Val

Returns the current Val of this global.

Panics

Panics if store does not own this global.

pub fn set(&self, store: impl AsContextMut, val: Val) -> Result<()>

Attempts to set the current value of this global to Val.

Errors

Returns an error if this global has a different type than Val, if it’s not a mutable global, or if val comes from a different store than the one provided.

Panics

Panics if store does not own this global.

Trait Implementations

impl Clone for Global

fn clone(&self) -> Global

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for Global

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

Formats the value using the given formatter.

impl From<Global> for Extern

fn from(r: Global) -> Self

Converts to this type from the input type.

impl Copy for Global