How to write a function to select a specific enum variant?

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1 
// prost-build, so not really changeable
mod generated_from_protobuf {
  struct MessageOneT {
    // something
  }
  struct MessageTwoT {
    // something
  }

  enum Messages {
    MessageOne(MessageOneT),
    MessageTwo(MessageTwoT),
    //100+ variants
  }
}

/// Waits for `Messages::MessageOne`, ignoring other variants of `Messages`
fn wait_for_msg_one() -> MessageOneT {
    loop {
        // would be received from a channel
        let incoming: Messages = Messages::MessageOne(MessageOneT {});

        // will have boilerplate for timeouts, etc.
        if let Messages::MessageOne(t) = incoming {
            return t;
        }
    }
}

// Any way to avoid writing one function per enum variant, but still having an easy way to wait for whatever variant is needed?

How can I make wait_for_msg_one work for all variants of the enum? Is there a way to write it so I can just say wait for the next MessageThree and it figures out that means it will return MessageThreeT? Ideally without writing something for each variant, as there's 100+ of them, and they will be added over time. Or is this something where macros would have to be used? (I've never written one)

2

You probably do want some sort of macro. Perhaps this one (but I didn't try it out or know the nuances around overlapping variant-wrapped types). Then you could

fn wait_for_msg<T: TryFrom<Messages>>() -> T {
    loop {
        let incoming: Messages = todo!();
        if let Ok(msg) = T::try_from(incoming) {
            return msg;
        }
    }
}
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