`block2 0.2.0-alpha.6`: Implementing `Encode`/`RefEncode` is bothersome and not always possible

[poliorcetics]

I tried using the alpha 6 of block2, which lead me to objc2_encode which asked me to implement Encode and RefEncode

1. It is bothersome to implement for the default case (a struct/union) with no particular semantics, in which case a derive proc macro could be provided.
2. When using types from libc, e.g. stat, I either have to stop and not implement the traits or I have to go deep to find if there are pointers/members to other structs where I have to do the same until I reach only base types. In the case of pointers I don't even know how I would do it ? A mimic struct defined locally which implements Encode ?

I don't know if there is a good solution to 2. sadly, because adding a dep in libc on objc2_encode is certainly not going to work.

[madsmtm]

Hey, it seems like this issue belongs in the objc2 repository.

There you will also find that a derive macro for Encode/RefEncode is being worked on (albeit low priority right now).

Also, you can "cheat" a bit with types like stat, and just use a c_void pointer in it's place:

use std::ffi::c_void;
use libc::stat;
use block2::ConcreteBlock;

let block = ConcreteBlock::new(|s: *const c_void| {
    let s: *const stat = s.cast();
    // Use `s` here
});
// ...