icu_provider

icu_provider is one of the ICU4X components.

Unicode's experience with ICU4X's parent projects, ICU4C and ICU4J, led the team to realize that data management is the most critical aspect of deploying internationalization, and that it requires a high level of customization for the needs of the platform it is embedded in. As a result ICU4X comes with a selection of providers that should allow for ICU4X to naturally fit into different business and technological needs of customers.

icu_provider defines traits and structs for transmitting data through the ICU4X locale data pipeline. The primary trait is [DataProvider]. It is parameterized by a [DataMarker], which is the type-system-level data identifier. [DataProvider] has a single method, [DataProvider::load], which transforms a [DataRequest] into a [DataResponse].

• [DataRequest] contains selectors to choose a specific variant of the marker, such as a locale.
• [DataResponse] contains the data if the request was successful.

The most common types required for this crate are included via the prelude:

use icu_provider::prelude::*;

Dynamic Data Providers

If the type system cannot be leveraged to load data (such as when dynamically loading from I/O), there's another form of the [DataProvider]: [DynamicDataProvider]. While [DataProvider] is parametrized on the type-system level by a [DataMarker] (which are distinct types implementing this trait), [DynamicDataProvider]s are parametrized at runtime by a [DataMarkerInfo] struct, which essentially is the runtime representation of the [DataMarker] type.

The [DynamicDataProvider] is still type-level parametrized by the type that it loads, and there are two implementations that should be called out

• [DynamicDataProvider<AnyMarker>], and AnyProvider (a slightly optimized alternative) return data as dyn Any trait objects.
• [DynamicDataProvider<BufferMarker>], a.k.a. BufferProvider returns data as [u8] buffers.

AnyProvider

These providers are able to return structured data cast into dyn Any trait objects. Users can call as_downcasting() to get an object implementing [DataProvider] by downcasting the trait objects.

Examples of AnyProviders:

• FixedProvider wraps a specific data struct and returns it.

BufferProvider

These providers are able to return unstructured data typically represented as [serde]-serialized buffers. Users can call as_deserializing() to get an object implementing [DataProvider] by invoking Serde Deserialize.

Examples of BufferProviders:

• FsDataProvider reads individual buffers from the filesystem.
• BlobDataProvider reads buffers from a large in-memory blob.

Provider Adapters

ICU4X offers several built-in modules to combine providers in interesting ways. These can be found in the icu_provider_adapters crate.

Testing Provider

This crate also contains a concrete provider for demonstration purposes:

• HelloWorldProvider returns "hello world" strings in several languages.

Types and Lifetimes

Types compatible with Yokeable can be passed through the data provider, so long as they are associated with a marker type implementing [DynamicDataMarker].

Data structs should generally have one lifetime argument: 'data. This lifetime allows data structs to borrow zero-copy data.

More Information

For more information on development, authorship, contributing etc. please visit ICU4X home page.