You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: lib.rs
    path of file: ./repos/xactor/src
    
    the code of the file until where you have to start completion: //! # Xactor is a rust actors framework based on async-std
//!
//! ## Documentation
//!
//! * [GitHub repository](https://github.c
    
//! async fn main() -> Result<()> {
//!     // Start actor and get its address
//!     let mut addr = MyActor.start().await?;
//!
//!     // Send message `ToUppercase` to actor via addr
//!     let res = addr.call(ToUppercase("lowercase".to_string())).await?;
//!     assert_eq!(res, "LOWERCASE");
//!     Ok(())
//! }