#[repr(C)]
pub struct FunctionKernel<T: Value>(fn(Call) -> JsResult<T>);

impl<T: Value> Kernel<()> for FunctionKernel<T> {
    extern "C" fn callback(info: &CallbackInfo) {
        info.scope().exec(info, |call| {
            let data = info.data();
            let FunctionKernel(kernel) = unsafe { Self::from_wrapper(data.to_raw()) };
//          error: the parameter type `T` might not live long enough
//          note: the parameter type `T` must be valid for the anonymous lifetime #1 defined on the block at 6:39...
            if let Ok(value) = kernel(call) {
//                             ~~~~~~~~~~~~
                info.set_return(value);
            }
        })
    }
    // ...
}

impl<'a> RootScopeInternal<'a> for RootScope<'a> {
    fn exec<T: 'a, U: This, F: FnOnce(FunctionCall<U>) -> T>(&'a mut self, info: &'a CallbackInfo, f: F) -> T {
        let mut v8_scope = raw::HandleScope::new();
        unsafe {
            neon_sys::scope::enter(&mut v8_scope, self.isolate().to_raw());
        }
        let call = info.as_call(self);
        let result = f(call);
        unsafe {
            neon_sys::scope::exit(&mut v8_scope);
        }
        result

    }
    // ...
}