---
title: Replies Overview
---

In Kameo, replies are the responses sent back from an actor following the receipt and processing of a message. These replies are fundamental to the ask pattern of actor communication, where a sender awaits a response to proceed. Ensuring that replies are properly structured and handled is crucial for maintaining the flow of information and control within your actor system.

## The Reply Trait

To facilitate communication within Kameo, all types intended to serve as responses from an actor must implement the `Reply` trait. This designation ensures that a type is recognized as a valid form of reply, capable of being processed within the actor's messaging system.

Special attention is given to replies that encapsulate a `Result::Err` variant from the Rust standard library. These are treated distinctively compared to their non-error counterparts. Specifically, when a message is dispatched using the "tell" method, any errors emerging from the actor's message handler are interpreted as panics. This mechanism highlights the critical role of thorough error handling and validation in an actor's message processing routine, safeguarding against unexpected terminations.

While most standard library types already implement the `Reply` trait, there might be exceptions. Should you encounter a standard library type not implementing `Reply`, you are encouraged to report this through an issue. For types outside the standard library that do not implement `Reply`, a straightforward workaround is to wrap your reply type in a `Result<T, kameo::error::Infallible>`, where `T` is your original type. Given that any `Result` type inherently implements `Reply`, this approach often obviates the need for custom implementations of the `Reply` trait for your types, especially in scenarios where using `Result` types is a common practice.

## Deriving the Reply Trait

Kameo simplifies the implementation of the `Reply` trait through the `#[derive(Reply)]` macro. This macro automatically provides the necessary trait implementations for a type, making it straightforward to create custom reply types that integrate seamlessly with Kameo's messaging system.

### Example Usage

```rust
use kameo::Reply;

#[derive(Reply)]
pub struct MyReply {
    pub data: String,
    pub status: bool,
}

// Usage within an actor
impl Message<MyRequest> for MyActor {
    type Reply = MyReply;

    async fn handle(
        &mut self,
        msg: MyRequest,
        _: Context<'_, Self, Self::Reply>,
    ) -> Self::Reply {
        // Logic to process the message and generate a reply
        MyReply {
            data: "Processed data".to_string(),
            status: true,
        }
    }
}
```

In this example, `MyReply` is defined as a struct with data relevant to the response expected by a sender. By deriving the `Reply` trait, `MyReply` is automatically equipped to serve as a response in Kameo's messaging system. This pattern allows for rich, structured data to be communicated back to senders, facilitating complex interactions and workflows within your actor system.

## Handling Replies

When dealing with ask requests, it's important to handle replies gracefully. This involves not only receiving the reply but also managing potential timeouts and errors that might occur during the interaction. If the message handler returned an error while processing a message, it will be returned as a `SendError::HandlerError`. Kameo's design encourages clear, concise handling of these scenarios, ensuring that your actor system remains robust and resilient under various operational conditions.

---

#### Summary

Replies play a crucial role in the communication loop between actors in Kameo, particularly when direct feedback or data needs to be conveyed back to the requester. They enrich the interaction model, enabling more structured and predictable exchanges. By defining clear and meaningful replies, you ensure smoother and more reliable communication flows, which is essential for handling complex and evolving workflows within your applications.
