wasmtime-callbacks.rs

struct StoreToken<T> {
    id: StoreId,
    _phantom: PhantomData<fn() -> T>, 
}
  
impl<T> StoreToken<T> {
    pub fn new(store: StoreContextMut<T>) -> Self {
        Self { id: store.id(), _phantom: PhantomData }
    }
  
    pub fn safe_cast<'a>(store: &'a mut dyn VMStore) -> StoreContextMut<'a, T> {
         assert_eq!(store.store_opaque().id(), id);
         // We know the store with this ID has data type parameter `T` because we witnessed that in `Self::new`:
         unsafe { StoreContextMut::<T>(&mut *(store as *mut dyn VMStore).cast()) }
    }
}
  
fn foo<T>(store: StoreContextMut<T>) { .. }
  
fn bar<T: 'static>(store: StoreContextMut<T>) -> Box<dyn Fn(&mut dyn VMStore) + Send + Sync + 'static {
    let token = StoreToken::new(store);
    Box::new(move |store| foo(token.safe_cast(store)))
}