Platforms

Where dxn_intl builds and runs, why it reads nothing from the system, the thread restrictions of its formatters, and how large the compiled-in locale data makes a WebAssembly build.

dxn_intl is pure Rust over ICU4X’s compiled data. It opens no files, reads no environment variable, asks for no clock and starts no thread, so the same code runs on every target Rust supports and in the browser. The caller supplies what the platform knows: the locale and the local wall time.

#Targets

The minimum Rust version is 1.97 (edition 2024); CI builds with 1.97 and develops on 1.99. There are no Cargo features, and unsafe code is forbidden in the crate (unsafe_code = "forbid").

CI also fails when a UI or app framework appears in the dependency tree: the crate stays independent of NSH, GPUI, RayX, Leptos, Dioxus and similar, and frameworks wrap it in their own repositories.

#What the platform has to give you

None of this is read for you, so a unit test can run on any machine with fixed inputs and print the same text.

#Browser and WebAssembly

The crate builds for wasm32-unknown-unknown with no extra crates and no JavaScript glue. It exports no wasm-bindgen API of its own; call it from your own exported functions.

rustup target add wasm32-unknown-unknown
cargo build --release --target wasm32-unknown-unknown

Because the formatting runs in Rust on the same data, a browser page shows the same text as the native app for the same locale and options, instead of depending on the browser’s own Intl implementation.

#Data size

The locale data is compiled into the binary (icu’s compiled data, with every locale), so there is nothing to fetch at run time, and the linker keeps only the data of the formatters you use: a program that only picks plural categories does not carry the date patterns. There is no Cargo feature to restrict the set of locales.

These sizes were measured while writing these docs at v0.1.0, with Rust 1.99, for a cdylib that calls one formatter and is built for wasm32-unknown-unknown with opt-level = "z", lto = true, codegen-units = 1, strip = true and panic = "abort":

The date and time formatter is by far the largest because of the calendars and the names of months, weekdays and eras in every language. Reproduce the measurement for your own build:

use dxn_intl::{DateTimeFormatter, DateTimeOptions, DateTime, Length, parse_locale};

#[unsafe(no_mangle)]
pub extern "C" fn format_length(day: u32) -> usize {
    let Ok(locale) = parse_locale("de") else { return 0 };
    let options = DateTimeOptions::date_time(Length::Long);
    let Ok(formatter) = DateTimeFormatter::new(&locale, options) else { return 0 };
    let Ok(moment) = DateTime::date(2026, 1, (day % 28 + 1) as u8) else { return 0 };
    formatter.format(&moment).map_or(0, |text| text.len())
}

Put it in a crate-type = ["cdylib"] library, build with the profile above and look at the size of target/wasm32-unknown-unknown/release/*.wasm. Compression on the wire (gzip or Brotli) shrinks it considerably; measure with your server’s settings.

#Threads

PluralRules, NumberFormatter and DateTimeFormatter are neither Send nor Sync. They hold ICU4X data behind Rc. In practice:

• A formatter stays on the thread that made it. In a multi-threaded runtime, build it inside the task that uses it, or keep it in a thread_local!.
• A GUI toolkit’s main thread is the natural owner of a per-locale set.
• Number, DateTime, Locale and IntlError are Send + Sync, so you can compute values on any thread and format them on the right one.

The cookbook shows a per-thread cache. Building a formatter took microseconds in a release build when measured while writing these docs, so building one per task is acceptable.

#ICU4X dependencies

icu_experimental is pinned with =0.7.0 because ICU4X may change its API in any release; the crate bumps it deliberately and reruns every test. If your own code also uses icu_experimental, depend on the same version. Locale and Number::as_decimal expose ICU4X types; everything else in the public API is this crate’s own.

#Next

Limitations lists what is not covered. Releases explains how versions are cut.