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: mod.rs
    path of file: ./repos/Fyrox/fyrox-sound/src/buffer
    
    the code of the file until where you have to start completion: //! This module provides all needed types and methods to create/load sound
    
    fn read(&mut self, buf: &mut [u8]) -> Result<usize, std::io::Error> {
        match self {
            DataSource::File { data, .. } => data.read(buf),
            DataSource::Memory(b) => b.read(buf),
            DataSource::Raw { .. } => unreachable!("Raw data source does not supports Read trait!"),
            DataSource::RawStreaming { .. } => {
                unreachable!("Raw data source does not supports Read trait!")
            }
        }
    }