Something I find myself often wanting to reach for in #rustlang is a `FnPtr` trait: akin to `Fn`/`FnMut`/etc. except where the function is guaranteed to be representable as a function pointer. There are many times when I want to carry something over, say, an FFI boundary without needing the caller of some API to explicitly pass a function pointer. 

 @cc9dd4bb Could you please explain the difference to a normal function pointer?

https://doc.rust-lang.org/std/primitive.fn.html