Expand description
§Overview
This is a simple set of functions to make your life easier while working with defaults in serde. Based on const generic parameters. Heavily inspired by discussions on issues about serde defaults, but mostly this one
§Kudos
- JohnTheCoolingFan posted this solution, I just made it available as crate and a macro that helps to generate another const generic function for any const generic type.
- bytedream made a more powerful version of it, and although I still see const generic approach as more readable, I have to admit that for strings it’s superior, hence - included under the feature
§Example
use serde_default_utils::*;
use serde::{Deserialize, Serialize};
const JSON: &str =
r#"{
"yes_or_no":false,
"max":60,
"delta":-77,
"delimeter":"☀",
"motto":"I matter"
}"#;
const INLINE_JSON: &str =
r#"{
"inline_motto":"I matter even more",
"slice":["I", "matter", "even", "more"],
"slice_u64":[9000, 8000, 10000, 7000]
}"#;
const EMPTY_JSON: &str = r#"{}"#;
const MAX: u32 = 7;
#[derive(Serialize, Deserialize, Default)]
struct Config {
#[serde(default = "default_bool::<true>")]
yes_or_no: bool,
#[serde(default = "default_i16::<-3>")]
delta: i16,
// you can even use consts right here
#[serde(default = "default_u32::<MAX>")]
max: u32,
#[serde(default = "default_char::<'☀'>")]
delimeter: char,
}
#[cfg(feature = "inline")]
#[serde_inline_default]
#[derive(Serialize, Deserialize, Default)]
struct InlineConfig {
#[serde_inline_default("You matter even more".to_string())]
inline_motto: String,
#[serde_inline_default(vec!["You".into(), "matter".into(), "even".into(), "more".into()])]
slice: Vec<String>,
#[serde_inline_default(vec![98712, 12346, 129389, 102937])]
slice_u64: Vec<u64>,
}
fn main() {
// existing json fields are not changed
let config: Config = serde_json::from_str(JSON).unwrap();
let s = serde_json::to_string(&config).unwrap();
assert_eq!(r#"{"yes_or_no":false,"delta":-77,"max":60,"delimeter":"☀"}"#, &s);
// if the field is not present - it is substituted with defaults
let config: Config = serde_json::from_str(EMPTY_JSON).unwrap();
let s = serde_json::to_string(&config).unwrap();
assert_eq!(r#"{"yes_or_no":true,"delta":-3,"max":7,"delimeter":"☀"}"#, &s);
// the default impl is just calling underlying type defaults unless you have a custom impl Default
let config = Config::default();
let s = serde_json::to_string(&config).unwrap();
assert_eq!(r#"{"yes_or_no":false,"delta":0,"max":0,"delimeter":"\u0000"}"#, &s);
// Inline
#[cfg(feature = "inline")]
{
// existing json fields are not changed
let config: InlineConfig = serde_json::from_str(INLINE_JSON).unwrap();
let s = serde_json::to_string(&config).unwrap();
assert_eq!(r#"{"inline_motto":"I matter even more","slice":["I","matter","even","more"],"slice_u64":[9000,8000,10000,7000]}"#, &s);
// if the field is not present - it is substituted with defaults
let config: InlineConfig = serde_json::from_str(EMPTY_JSON).unwrap();
let s = serde_json::to_string(&config).unwrap();
assert_eq!(r#"{"inline_motto":"You matter even more","slice":["You","matter","even","more"],"slice_u64":[98712,12346,129389,102937]}"#, &s);
// the default impl is just calling underlying type defaults unless you have a custom impl Default
let config = InlineConfig::default();
let s = serde_json::to_string(&config).unwrap();
assert_eq!(r#"{"inline_motto":"","slice":[],"slice_u64":[]}"#, &s);
}
}
Macros§
- serde_
default - Generates a function for a type provided or a custom default function This is not supposed to be used outside since const generic parameter approach is pretty limited at the moment