Struct Update Syntax with Default

Snippet

Struct Update Syntax with Default

Rust's struct update syntax using `..` allows you to create a new struct instance while copying most fields from an existing one. Combined with the `Default` derive macro, it enables efficient configuration patterns where you start with a base configuration and override only specific fields.

snippet.rs
rust
#[derive(Default, Debug)]
struct Config {
    host: String,
    port: u16,
    timeout: u64,
}
 
fn main() {
    let base = Config {
        host: String::from("localhost"),
        port: 8080,
        timeout: 30,
    };
 
    
    let override_config = Config {
        timeout: 60,
        ..base
    };
    
    println!("{:?}", override_config);
}

Breakdown

#[derive(Default, Debug)]

Derive macro that implements Default trait for zero-value initialization and Debug for printing

struct Config { host: String, port: u16, timeout: u64 }

Struct definition with three fields: host (String), port (u16), and timeout (u64)

let base = Config { host: String::from("localhost"), port: 8080, timeout: 30 }

Create a base configuration instance with default values for all fields

let override_config = Config { timeout: 60, ..base }

Create a new config by overriding only timeout, copying host and port from base

println!("{:?}", override_config)

Print the override_config using Debug formatting: Config { host: "localhost", port: 8080, timeout: 60 }

Previous snippet Next snippet

More Intermediate Rust exercises →

From your library

Struct Update Syntax with Default

Related