I'm having a bit of trouble moving my previously RefCell'ed code into a thread safe world. I'm coming across an error that has to do with dyn Traits, and I don't think the compiler is giving me that useful of information.
I saw and read a couple of posts on impl vs dyn, but I think this more has to do with the containers of Box, Muted, and Arc.
In the link below I have my previous implentation that works and the new impl that's doesn't. Any help would be appreciated.
This compiles on the playground:
enum SafeFile<'a> {
UserDefined(Arc<Mutex<dyn Read + 'a>>),
}
impl SafeFile<'_> {
fn write(&mut self /* and writer, etc */) {
match self {
SafeFile::UserDefined(file) => {
let c = Arc::clone(file);
let l = file.lock().unwrap();
- add_bytes(*l);
+ add_bytes(&*l);
}
}
}
}
fn safe_one<'a>(reader: impl Read + 'a) {
let reader = Arc::new(Mutex::new(reader));
let file = SafeFile::UserDefined(reader);
}
// same for both
- fn add_bytes(reader: impl Read /* and writer */) {
+ fn add_bytes(reader: &(impl Read + ?Sized) /* and writer */) {
todo!()
}
We have to relax the implicit Sized requirement (because trait objects are dynamically sized) and need to provide the trait object as reference (because we can't pass dynamically sized types around).
This also works, without changing the definition of add_bytes, because &mut R implements Read whenever R does:
impl SafeFile<'_> {
fn write(&mut self /* and writer, etc */) {
match self {
SafeFile::UserDefined(file) => {
let c = Arc::clone(file);
- let l = file.lock().unwrap();
- add_bytes(*l);
+ let mut l = file.lock().unwrap();
+ add_bytes(&mut *l);
}
}
}
}