README.md - mozsearch

# icu_provider [![crates.io](https://img.shields.io/crates/v/icu_provider)](https://crates.io/crates/icu_provider)

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`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

[`KeyedDataMarker`], which contains the data type and a [`DataKey`]. It has one method,

[`DataProvider::load`], which transforms a [`DataRequest`]

into a [`DataResponse`].

- [`DataKey`] is a fixed identifier for the data type, such as `"plurals/cardinal@1"`.

- [`DataRequest`] contains additional annotations to choose a specific variant of the key,

  such as a locale.

- [`DataResponse`] contains the data if the request was successful.

In addition, there are three other traits which are widely implemented:

- [`AnyProvider`] returns data as `dyn Any` trait objects.

- [`BufferProvider`] returns data as `[u8]` buffers.

- [`DynamicDataProvider`] returns structured data but is not specific to a key.

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

```rust

use icu_provider::prelude::*;

```

### Types of Data Providers

All nontrivial data providers can fit into one of two classes.

1. [`AnyProvider`]: Those whose data originates as structured Rust objects

2. [`BufferProvider`]: Those whose data originates as unstructured `[u8]` buffers

**✨ Key Insight:** A given data provider is generally *either* an [`AnyProvider`] *or* a

[`BufferProvider`]. Which type depends on the data source, and it is not generally possible

to convert one to the other.

See also [crate::constructors].

#### 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:

- [`DatagenProvider`] reads structured data from CLDR source files and returns ICU4X data structs.

- [`AnyPayloadProvider`] wraps a specific data struct and returns it.

- The `BakedDataProvider` which encodes structured data directly in Rust source

#### 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 [`DataMarker`].

Data structs should generally have one lifetime argument: `'data`. This lifetime allows data

structs to borrow zero-copy data.

### Data generation API

*This functionality is enabled with the "datagen" Cargo feature*

The [`datagen`] module contains several APIs for data generation. See [`icu_datagen`] for the reference

data generation implementation.

[`ICU4X`]: ../icu/index.html

[`DataProvider`]: data_provider::DataProvider

[`DataKey`]: key::DataKey

[`DataLocale`]: request::DataLocale

[`IterableDynamicDataProvider`]: datagen::IterableDynamicDataProvider

[`IterableDataProvider`]: datagen::IterableDataProvider

[`AnyPayloadProvider`]: ../icu_provider_adapters/any_payload/struct.AnyPayloadProvider.html

[`HelloWorldProvider`]: hello_world::HelloWorldProvider

[`AnyProvider`]: any::AnyProvider

[`Yokeable`]: yoke::Yokeable

[`impl_dynamic_data_provider!`]: impl_dynamic_data_provider

[`icu_provider_adapters`]: ../icu_provider_adapters/index.html

[`DatagenProvider`]: ../icu_datagen/struct.DatagenProvider.html

[`as_downcasting()`]: AsDowncastingAnyProvider::as_downcasting

[`as_deserializing()`]: AsDeserializingBufferProvider::as_deserializing

[`CldrJsonDataProvider`]: ../icu_datagen/cldr/struct.CldrJsonDataProvider.html

[`FsDataProvider`]: ../icu_provider_fs/struct.FsDataProvider.html

[`BlobDataProvider`]: ../icu_provider_blob/struct.BlobDataProvider.html

[`icu_datagen`]: ../icu_datagen/index.html

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## More Information

For more information on development, authorship, contributing etc. please visit [`ICU4X home page`](https://github.com/unicode-org/icu4x).