I am trying to implement a declarative macro that, given a type, implements a recursive asynchronous function that takes that type as parameter. However, it seems unfeasible when the given type is a reference, since the type may not live as long as the 'async_recursion lifetime.

A minimal example of the declarative macros is something as following:

macro_rules! help_please {
    ($param:ty) => {
        #[async_recursion]
        async fn recursive_fn<F>(param: $param, f: &F)
        where
            F: Fn($param) + Sync + Send,
        {
            f(param);
        }
    };
}

And then, if I use it like in the example down below, it does not compile and tells me to add explicit lifetime 'async_recursion to the type of 'param': &'async_recursion usize. What cannot be done since the lifetime `async_recursion does not exist at that level.

macros_async::help_please!(&usize);

I am aware that my approach may be weird or absolutely wrong; however, I would like to know if there is any way to tell async_recursion which is the lifetime that should be taken as `async_recursion. Can this situation be resolved somehow? Thanks in advance!