Crate day_part_prefs 

day-part-prefs — a HEADLESS cross-platform persistent key/value store. No UI; any Rust code can depend on this crate and call set / get / remove / contains to persist small strings across launches through the platform’s NATIVE preferences facility.

day_part_prefs::set("greeting", "hello");
assert_eq!(day_part_prefs::get("greeting").as_deref(), Some("hello"));
assert!(day_part_prefs::contains("greeting"));
day_part_prefs::remove("greeting");

Platform selection is purely #[cfg(target_os)]/#[cfg(target_env)] (persistence is an OS concern, not a widget-toolkit one): macOS and iOS share one NSUserDefaults file, Android uses SharedPreferences (via a Java shim staged by day build), and Linux / Windows / HarmonyOS share a file-backed store under the per-user config directory. Values persist until removed and survive process restarts. Platforms without any store fall back to a no-op that always reports failure/absence.

This is a small string store for user settings and lightweight app state — not a database. Keep values modest; large blobs belong in a file. See docs/prefs.md for the per-platform matrix.

Functions

bind

Two-way-bind a signal to a stored preference: seed the signal from the store now (when a stored value exists and parses as T), then persist every later change. Call it right after creating the signal, before anything reads it. The write-back lives in the current reactive scope, so it stops with the page that created the signal.

contains

Whether a value is currently stored under key.

get

Read the string stored under key, or None if it is absent (or no store is available on the platform). A stored empty string is Some(""), distinct from an absent key.

install_nav_store

Install this prefs store as the app’s navigation-persistence store (docs/navigation.md), so a selector or stack marked .restore(key) remembers its state across launches (and across an Android process death, since the store is disk-backed). Call once at startup, before the UI mounts. Nav keys are namespaced under a day.nav. prefix, so .restore("mail") never collides with the app’s own set/get keys.

remove

Delete the value stored under key. Returns true if a value existed and was removed, false if the key was already absent (or the delete could not be committed).

set

Persist value under key, overwriting any previous value. Returns true when the write was committed. On Apple platforms this always succeeds; on Android it reflects SharedPreferences.Editor.commit(); on the file-backed platforms it reflects whether the store file could be written (a missing config directory or a read-only home yields false).