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: mapper_003.rs
    path of file: ./repos/nestadia/nestadia/src/cartridge
    
    the code of the file until where you have to start completion: use super::{CartridgeReadTarget, Mapper, Mirroring};

pub struct Mapper003 {
    chr_bank_selector: u8,
    prg_ban
    
    fn get_prg_bank(&self, addr: u16) -> Option<u8> {
        match addr {
            0x8000..=0xBFFF => Some(0),
            0xC000..=0xFFFF => Some(1),
            _ => None,
        }
    }