facet-default

facet-default

Derive Default for your types using facet's plugin system with custom field defaults.

Usage

use facet::Facet;
use facet_default as default;

#[derive(Facet, Debug)]
#[facet(derive(Default))]
pub struct Config {
    #[facet(default::value = "localhost")]
    host: String,
    #[facet(default::value = 8080u16)]
    port: u16,
    #[facet(default::func = "default_timeout")]
    timeout: std::time::Duration,
    // No attribute = uses Default::default()
    debug: bool,
}

fn default_timeout() -> std::time::Duration {
    std::time::Duration::from_secs(30)
}

Attributes

Field Level

• #[facet(default::value = literal)] - Use a literal value (converted via .into())
• #[facet(default::func = "path")] - Call a function to get the default value

Fields without attributes use Default::default().

Note: For numeric literals, use type suffixes to ensure correct types (e.g., 8080u16 instead of 8080 for a u16 field). String literals are automatically converted via .into().

Enums

For enums, mark the default variant with #[facet(default::variant)]:

use facet::Facet;
use facet_default as default;

#[derive(Facet, Debug, PartialEq)]
#[facet(derive(Default))]
#[repr(u8)]
pub enum Status {
    #[facet(default::variant)]
    Pending,
    Active,
    Done,
}

assert_eq!(Status::default(), Status::Pending);

Enum variants with fields also work - fields use their own default attributes:

use facet::Facet;
use facet_default as default;

#[derive(Facet, Debug)]
#[facet(derive(Default))]
#[repr(u8)]
pub enum Request {
    #[facet(default::variant)]
    Get {
        #[facet(default::value = "/")]
        path: String,
        #[facet(default::value = 80u16)]
        port: u16,
    },
    Post { path: String, body: String },
}

LLM contribution policy

Sponsors

Thanks to all individual sponsors:

...along with corporate sponsors:

...without whom this work could not exist.

Special thanks

The facet logo was drawn by Misiasart.

License

Licensed under either of:

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.