icu_provider

icu_provider is one of the ICU4X components.

It defines traits and structs for transmitting data through the ICU4X locale data pipeline. The primary trait is DataProvider. It has one method, which transforms a Request into a Response:

fn load_payload(&self, req: &DataRequest) -> Result<DataResponse<'d>, DataError>

A Request contains a ResourceKey (a composition of a Category and sub-category, e.g., "plurals/cardinal@1") and ResourceOptions (a language identifier and optional variant, e.g., "fr") being requested. The Response contains the data payload corresponding to the Request.

The most common types required for ICU4X DataProvider are included via the prelude:

use icu_provider::prelude::*;

Concrete Implementations of Data Providers

Any object implementing DataProvider can be used to supply ICU4X with locale data. ICU4X ships with some pre-built data providers:

• CldrJsonDataProvider reads structured data directly from CLDR source files.
• FsDataProvider reads structured data from the filesystem. It can also write out that filesystem structure. More efficient than CldrJsonDataProvider.

This crate also contains some concrete implementations for testing purposes:

• InvariantDataProvider returns fixed data that does not vary by locale.
• StructProvider wraps a particular instance of a struct and returns it.
• HelloWorldProvider returns "hello world" strings in several languages.

Types and Lifetimes

All types T compatible with Cow and Debug can be passed through the data provider.

Most DataProvider traits take a lifetime argument 'd. This represents the lifetime of data returned by the DataProvider, which is a Cow<'d, T>.

Objects returned by DataProvider can have their own borrowed fields, which enables zero-copy deserialization. By convention, the lifetime 's is used to constrain data struct fields. In general, 's should exceed 'd (i.e., 's: 'd), such that the data is valid for as long as the Cow<'d, T> is valid.

Additional Traits

IterableDataProvider

Data providers can implement IterableDataProvider, allowing iteration over all ResourceOptions instances supported for a certain key in the data provider.

For more information, see the [iter] module.

SerdeDeDataProvider

Enabled with the "provider_serde" feature

The trait SerdeDeDataProvider removes the type argument from DataProvider and requires that all data structs be deserializable via Serde. This allows for a Serde-enabled provider to be saved as a trait object without being specific to a data struct type.

DataProvider<dyn SerdeSeDataStruct>

Enabled with the "provider_serde" feature

Data providers capable of returning opaque SerdeSeDataStruct trait objects can be used as input to a data exporter, such as when writing data to the filesystem.

This trait is normally implemented using the impl_dyn_provider! macro.

DataProvider<dyn ErasedDataStruct>

The trait ErasedDataProvider removes the type argument from DataProvider and requires that all data structs be convertible to the Any type. This enables the processing of data without the caller knowing the underlying data struct.

Since ErasedDataProvider is not specific to a single type, it can be useful for caches or other bulk data operations.

This trait is normally implemented using the impl_dyn_provider! macro.

More Information

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