wasm-ref-cell.rs

pub struct WasmRefCell<T>(core::cell::RefCell<T>);

impl<T> WasmRefCell<T> {
    pub const fn new(initial_value: T) -> WasmRefCell<T> {
        WasmRefCell(core::cell::RefCell::new(initial_value))
    }

    pub fn with<U, F: FnOnce(&mut T) -> U>(&self, f: F) -> U {
        f(&mut *self.0.borrow_mut())
    }
}

#[cfg(target_arch = "wasm32")]
mod wasm32_has_no_threads {
    unsafe impl<T> Send for super::WasmRefCell<T> {}
    unsafe impl<T> Sync for super::WasmRefCell<T> {}
}

pub struct GlobalContext {
    spam: i32,
}

impl GlobalContext {
    pub fn with<T, F: FnOnce(&mut GlobalContext) -> T>(f: F) -> T {
        static INSTANCE: WasmRefCell<GlobalContext> = WasmRefCell::new(GlobalContext { spam: 0 });
        INSTANCE.with(f)
    }
}