---
title: Getting Started
---

Welcome to Kameo, your gateway to building efficient, scalable, and resilient systems in Rust. This guide will walk you through the initial steps of installing Kameo and creating a simple "Hello, World!" application to get your feet wet in the world of asynchronous actors.

## Installation

Before diving into the world of Kameo, you'll need to ensure that your Rust development environment is set up. Kameo requires Rust 1.79, which you can install or update via [rustup](https://rustup.rs/).

With Rust installed, you can add Kameo to your project by editing your `Cargo.toml` file:

```toml
[dependencies]
kameo = "0.10.0" # Use the latest version
```

Alternatively you can run `cargo add kameo`.

## Hello World Actor

This example demonstrates a basic "Hello World" actor capable of handling a `Greet` message. It showcases the fundamental concepts of actor creation, message definition, and asynchronous message handling within Kameo.

### Defining the Actor and Message

First, we define a `HelloWorldActor` and a `Greet` message. The actor will process messages of type `Greet`, which contain a string greeting.

```rust
use kameo::Actor;
use kameo::message::{Message, Context};

// Define the actor
#[derive(Actor)]
pub struct HelloWorldActor;

// Define the message
pub struct Greet(String);

// Implement the message handling for HelloWorldActor
impl Message<Greet> for HelloWorldActor {
    type Reply = (); // This actor sends no reply

    async fn handle(
        &mut self,
        Greet(greeting): Greet, // Destructure the Greet message to get the greeting string
        _: Context<'_, Self, Self::Reply>, // The message handling context
    ) -> Self::Reply {
        println!("{greeting}"); // Print the greeting to the console
    }
}
```

### Spawning the Actor and Sending a Message

To interact with the `HelloWorldActor`, we spawn it and send a `Greet` message. This is done using the `spawn` function from Kameo and the `tell` method provided by the actor's reference, `actor_ref`.

```rust
use kameo::spawn;

#[tokio::main] // Mark the entry point as an asynchronous main function
async fn main() -> Result<(), Box<dyn std::error::Error>> { // Use a Result return type for error handling
    // Spawn the HelloWorldActor
    let actor_ref = spawn(HelloWorldActor);

    // Send a Greet message to the actor
    actor_ref
        .tell(Greet("Hello, world!".to_string()))
        .await?;

    Ok(())
}
```

### Understanding the Code

- **Actor Definition**: The `HelloWorldActor` is a simple actor that does not maintain any state and only prints out the greeting it receives.
- **Message Handling**: The `handle` method asynchronously processes the `Greet` message. It takes ownership of the message and a context parameter, which could be used for more advanced message handling scenarios.
- **Spawning and Messaging**: The `spawn` function creates an instance of the `HelloWorldActor` and returns a reference to it (`actor_ref`). The `tell` method is then used to send a `Greet` message to the actor. The `send` method is awaited to ensure the message is sent to the actors mailbox.
- **Asynchronous Runtime**: The example uses Tokio as the asynchronous runtime, indicated by the `#[tokio::main]` attribute. This is necessary for running asynchronous Rust code.

---

#### Next Steps

This example is a starting point for building applications with Kameo. From here, you can explore more complex actor behaviors, state management, actor supervision, and building distributed systems with remote actors.

Remember, the power of actors comes from their ability to encapsulate state and behavior, process messages concurrently, and interact in a decoupled manner. Experiment with these concepts to build scalable and resilient applications.
