Caching function handles in a struct, is it possible?

[IamTheCarl]

So I would like to do the following:

pub struct WasmFile {
    wasm_instance: Instance,

    // Several functions we plan to call frequently.
    __spawn_dynamic_entity: Func<u32, u64>,
    __drop_dynamic_entity: Func<u64, ()>,
}

I create a struct which contains an instance, and I cache handles to two functions I call often.
Of course this can't compile, because those two function handles are references to wasm_instance. Self referencing structs are not permitted in Rust, for a good reason of course.
I've experimented with using pins, NonNull, and some unsafe blocks, but I can't solve the lifetimes requirements of the function handles.

The documentation clearly states that using these handles to call, rather than doing instance.exports.get for every call will be faster, so I'd like to do this for my frequently called functions.

So what I'm wondering is... is something like this possible? Or will I be forced to have my instance live outside of the WasmFile struct?

[IamTheCarl]

Here's a working example of where I want to employ this.
https://github.com/IamTheCarl/grid_engine/blob/a2f162972f00706394dd06ad97cf0fbfb2f1e601/native/common/src/wasm.rs#L104

Currently I just get the function every time I need it, which works, but I suspect brings some unnecessary overhead.