/// However, a direct cast back is not possible. You need to use `transmute`:
///
/// ```rust
+/// # #[cfg(not(miri))] { // FIXME: use strict provenance APIs once they are stable, then remove this `cfg`
/// # let fnptr: fn(i32) -> i32 = |x| x+2;
/// # let fnptr_addr = fnptr as usize;
/// let fnptr = fnptr_addr as *const ();
/// let fnptr: fn(i32) -> i32 = unsafe { std::mem::transmute(fnptr) };
/// assert_eq!(fnptr(40), 42);
+/// # }
/// ```
///
/// Crucially, we `as`-cast to a raw pointer before `transmute`ing to a function pointer.