Shared via Rust Playground

playground.rs

#![feature(unboxed_closures, fn_traits)]

fn get_fn_ptr<C: Fn() -> ()>(_: &C) -> extern "rust-call" fn(&(), ()) -> () {
    let fn_ptr: extern "rust-call" fn(&(), ()) -> () = unsafe { std::mem::transmute(<C as std::ops::Fn<()>>::call as usize) };
    fn_ptr
}

fn main() {
    let closure = ||{ println!("hi") };
    let ptr = get_fn_ptr(&closure);
    ptr(&(), ());
}