Struct LocaleFallbackConfig

#[non_exhaustive]
pub struct LocaleFallbackConfig {
    pub priority: LocaleFallbackPriority,
    pub extension_key: Option<Key>,
    pub fallback_supplement: Option<LocaleFallbackSupplement>,
}

Configuration settings for a particular fallback operation.

Fields (Non-exhaustive)

Non-exhaustive structs could have additional fields added in future. Therefore, non-exhaustive structs cannot be constructed in external crates using the traditional Struct { .. } syntax; cannot be matched against without a wildcard ..; and struct update syntax will not work.

priority: LocaleFallbackPriority

Strategy for choosing which subtags to drop during locale fallback.

Examples

Retain the language and script subtags until the final step:

use icu::locid::locale;
use icu::locid_transform::fallback::LocaleFallbackConfig;
use icu::locid_transform::fallback::LocaleFallbackPriority;
use icu::locid_transform::LocaleFallbacker;

// Set up the fallback iterator.
let fallbacker = LocaleFallbacker::new();
let mut config = LocaleFallbackConfig::default();
config.priority = LocaleFallbackPriority::Language;
let mut fallback_iterator = fallbacker
    .for_config(config)
    .fallback_for(locale!("ca-ES-valencia").into());

// Run the algorithm and check the results.
assert_eq!(fallback_iterator.get(), &locale!("ca-ES-valencia").into());
fallback_iterator.step();
assert_eq!(fallback_iterator.get(), &locale!("ca-ES").into());
fallback_iterator.step();
assert_eq!(fallback_iterator.get(), &locale!("ca-valencia").into());
fallback_iterator.step();
assert_eq!(fallback_iterator.get(), &locale!("ca").into());
fallback_iterator.step();
assert_eq!(fallback_iterator.get(), &locale!("und").into());

Retain the region subtag until the final step:

use icu::locid::locale;
use icu::locid_transform::fallback::LocaleFallbackConfig;
use icu::locid_transform::fallback::LocaleFallbackPriority;
use icu::locid_transform::LocaleFallbacker;

// Set up the fallback iterator.
let fallbacker = LocaleFallbacker::new();
let mut config = LocaleFallbackConfig::default();
config.priority = LocaleFallbackPriority::Region;
let mut fallback_iterator = fallbacker
    .for_config(config)
    .fallback_for(locale!("ca-ES-valencia").into());

// Run the algorithm and check the results.
assert_eq!(fallback_iterator.get(), &locale!("ca-ES-valencia").into());
fallback_iterator.step();
assert_eq!(fallback_iterator.get(), &locale!("ca-ES").into());
fallback_iterator.step();
assert_eq!(fallback_iterator.get(), &locale!("und-ES-valencia").into());
fallback_iterator.step();
assert_eq!(fallback_iterator.get(), &locale!("und-ES").into());
fallback_iterator.step();
assert_eq!(fallback_iterator.get(), &locale!("und").into());

extension_key: Option<Key>

An extension keyword to retain during locale fallback.

Examples

use icu::locid::locale;
use icu::locid_transform::fallback::LocaleFallbackConfig;
use icu::locid_transform::LocaleFallbacker;

// Set up the fallback iterator.
let fallbacker = LocaleFallbacker::new();
let mut config = LocaleFallbackConfig::default();
config.extension_key = Some(icu::locid::extensions::unicode::key!("nu"));
let mut fallback_iterator = fallbacker
    .for_config(config)
    .fallback_for(locale!("ar-EG-u-nu-latn").into());

// Run the algorithm and check the results.
assert_eq!(fallback_iterator.get(), &locale!("ar-EG-u-nu-latn").into());
fallback_iterator.step();
assert_eq!(fallback_iterator.get(), &locale!("ar-EG").into());
fallback_iterator.step();
assert_eq!(fallback_iterator.get(), &locale!("ar-u-nu-latn").into());
fallback_iterator.step();
assert_eq!(fallback_iterator.get(), &locale!("ar").into());
fallback_iterator.step();
assert_eq!(fallback_iterator.get(), &locale!("und").into());

fallback_supplement: Option<LocaleFallbackSupplement>

Fallback supplement data key to customize fallback rules.

For example, most data keys for collation add additional parent locales, such as “yue” to “zh-Hant”, and data used for the "-u-co" extension keyword fallback.

Currently the only supported fallback supplement is LocaleFallbackSupplement::Collation, but more may be added in the future.

Examples

use icu::locid::locale;
use icu::locid_transform::fallback::LocaleFallbackConfig;
use icu::locid_transform::fallback::LocaleFallbackPriority;
use icu::locid_transform::fallback::LocaleFallbackSupplement;
use icu::locid_transform::LocaleFallbacker;

// Set up the fallback iterator.
let fallbacker = LocaleFallbacker::new();
let mut config = LocaleFallbackConfig::default();
config.priority = LocaleFallbackPriority::Collation;
config.fallback_supplement = Some(LocaleFallbackSupplement::Collation);
let mut fallback_iterator = fallbacker
    .for_config(config)
    .fallback_for(locale!("yue-HK").into());

// Run the algorithm and check the results.
assert_eq!(fallback_iterator.get(), &locale!("yue-HK").into());
fallback_iterator.step();
assert_eq!(fallback_iterator.get(), &locale!("yue").into());
fallback_iterator.step();
assert_eq!(fallback_iterator.get(), &locale!("zh-Hant").into());
fallback_iterator.step();
assert_eq!(fallback_iterator.get(), &locale!("zh").into());
fallback_iterator.step();
assert_eq!(fallback_iterator.get(), &locale!("und").into());