Hands-On Microservices with Rust

Joining all values by a priority

Our server has four sources of address settings:

• The configuration file
• The environment variable
• The command-line parameter
• The default value

We have to join these in this order. It's simple to implement this using a set of options and using the or method to set a value if the option doesn't contain anything. Use the following code to get address values from all of the sources:

let addr = matches.value_of("address")    .map(|s| s.to_owned())    .or(env::var("ADDRESS").ok())    .and_then(|addr| addr.parse().ok())    .or(config.map(|config| config.address))    .or_else(|| Some(([127, 0, 0, 1], 8080).into()))    .unwrap();

At first, this code takes a value from the --address command-line parameter. If it doesn't contain any ...