Is structure without methods which take mutable reference sync and send?


Let’s say I have a structure which only sends a request over the network. It has some fields but they can’t be changed since initialization because the structure’s implementation has no methods which take a mutable reference to the object but has one method which does it by move:

pub struct Client {
    client: reqwest::Client,
    keys: (String, String, String),
    oauth_token: Mutex<RefCell<AccessToken>>,
impl Client {
    fn (&self) -> Result<Object, Error>;
    // .... other methods like above
    fn (mut self) -> Self;

So, questions:

  1. Is this structure Send and Sync?
  2. Should I implement Send and Sync manually for them by using unsafe impl or they are derived automatically if the structure can be such?


Whether the Sync and Send traits are derived for a struct does not depend on the existens of &mut self methods, it is purely determined by the members.

In general, do not implement them manually! There is a reason for types to not implement them, and ignoring that will lead to soundness bugs.

To check whether a struct is Send or Sync, use them accordingly or check it like this:

fn assert_sync<T: Sync>() {}


There’s more information in the Rustonomicon.


That’s kind of unusual. It’s typical to use either Mutex or RefCell for interior mutability, but I don’t think there’s any purpose in using both.


Oh, yes, thanks much. I thought Mutex does not allow to change the object inside somewhy.