CODEWITHSUNDEEP
rust
dessalines
dessalines

Reputation: 7372

Update / re-initialize a var defined in lazy_static

I have a config that I want initialized on startup, but not have to re-read the file every time. To do this, I'm using lazy_static:

lazy_static! {
  static ref SETTINGS: Settings = {
    match Settings::init() {
      Ok(c) => c,
      Err(e) => panic!("{}", e),
    }
  };
}

But now I have a method that updates that config file, and I want to "re-initialize" / update it, without having to re-start the program.

  pub fn save_config_file(data: &str) -> Result<String, Error> {
    fs::write(CONFIG_FILE, data)?;
    SETTINGS = {
      match Settings::init() {
        Ok(c) => c, // The line with the error
        Err(e) => panic!("{}", e),
      }
    };

    Self::read_config_file()
  }

Which gives me the error: [rustc E0308] [E] mismatched types expected struct settings::SETTINGS, found struct settings::Settings

Is there any way to re-initialize a lazy_static? Or do I have to restart the program?

Upvotes: 3

Views: 2993

Answers (1)

dessalines
dessalines

Reputation: 7372

Okay, figured this one out. Mainly from here: How do I assign a String to a mutable static variable?

Add derive Clone to your struct:

#[derive(Debug, Deserialize, Clone)]

Wrap your lazy_static in an RwLock, initialize it normally.

use std::sync::RwLock;

lazy_static! {
  static ref SETTINGS: RwLock<Settings> = RwLock::new(
    match Settings::init() {
      Ok(c) => c,
      Err(e) => panic!("{}", e),
    }
  );
}

To read, you can do this:

  pub fn get() -> Self {
    SETTINGS.read().unwrap().to_owned()
  }

To write: 

    let mut new_settings = SETTINGS.write().unwrap();
    *new_settings = match Settings::init() {
      Ok(c) => c,
      Err(e) => panic!("{}", e),
    };

Upvotes: 4

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