Passing various unboxed closures to function w/ GATs

[wuavcv]

I previously got help with this unboxed closure issue by creating several implementations:

With the Stabilization of GATs, is there any way to combine these 3 implementations? Thanks!

Working code...

use wasm_bindgen::closure::Closure;

/* POC: Use traits instead of nested calls
 * i.e.
 * let x = myFn.set_closure_fnmut();
 * instead of
 * let x = Closure::wrap(Box::new(myFn) as Box<dyn FnMut(Event)>);
 */

pub trait SetClosureFnOnce<Dyn: ?Sized> {
    fn set_closure_fnonce(self) -> Closure<Dyn>;
}

impl<F> SetClosureFnOnce<dyn FnMut()> for F
where
    F: FnOnce() + 'static,
{
    fn set_closure_fnonce(self) -> Closure<dyn FnMut()> {
        let cb_boxed = Box::new(self) as Box<dyn FnOnce()>;
        Closure::once(cb_boxed)
    }
}

pub trait SetClosureFnMut<Dyn: ?Sized> {
    fn set_closure_fnmut(self) -> Closure<Dyn>;
}

impl<F> SetClosureFnMut<dyn FnMut()> for F
where
    F: FnMut() + 'static,
{
    fn set_closure_fnmut(self) -> Closure<dyn FnMut()> {
        let cb_boxed = Box::new(self) as Box<dyn FnMut()>;
        Closure::wrap(cb_boxed)
    }
}

impl<F, A, R> SetClosureFnMut<dyn FnMut(A) -> R> for F
where
    F: FnMut(A) -> R + 'static,
    A: wasm_bindgen::convert::FromWasmAbi + 'static,
    R: wasm_bindgen::convert::IntoWasmAbi + 'static,
{
    fn set_closure_fnmut(self) -> Closure<dyn FnMut(A) -> R> {
        let cb_boxed = Box::new(self) as Box<dyn FnMut(A) -> R>;
        Closure::wrap(cb_boxed)
    }
}

[H2CO3]

I'm not sure how GATs would help – neither of these traits has any associated types.

Are you trying to specify that if any given function/closure type F implements Fn, then the wrapper should wrap dyn Fn, if it's FnMut, then the wrapper should be dyn FnMut, etc.? Because that likely requires specialization.

[wuavcv]

The goal was a function that does:
Input: unboxed closure
Output: boxed closure

But since the closures come in different forms (Fn, FnOnce, FnMut), I have to have these varying implementations.

[H2CO3]

Yes, that's exactly what I suspected. I still don't think GATs solve this, because you want different impls for different, overlapping traits.

[wuavcv]

OK. Thanks!