Working with multiple crates in one library

Some teams arrange their Rust library in to multiple crates, or multiple teams from one organization combine their efforts into one library.

This might be for better code organization, or to reduce shipping multiple copies of the same dependencies.

The combined library from multiple crates, in Mozilla vernacular, is known as a Megazord.

uniffi-rs and uniffi-bindgen-react-native both work well with Megazords.

uniffi-bindgen-react-native produces a cluster of files per crate. For example, generating files from the library libmymegazord.a might contain two crates, crate1 and crate2. The library directory would look like this:

cpp
├── generated
│   ├── crate1.cpp
│   ├── crate1.hpp
│   ├── crate2.cpp
│   └── crate2.hpp
├── react-native-my-megazord.cpp
└── react-native-my-megazord.h
src
├── NativeMyMegazord.ts
├── generated
│   ├── crate1.ts
│   ├── crate1-ffi.ts
│   ├── crate2.ts
│   └── crate2-ffi.ts
└── index.tsx

In index.tsx, the types are re-exported from crate1.ts and crate2.ts.

In this extended example, crate1.ts might declare a Crate1Type and crate2.ts a Crate2Type.

In this case, your library’s client code would import Crate1Type and Crate2Type like this:

import { Crate1Type, Crate2Type } from "react-native-my-megazord";

Alternatively, they can use the default export:

import megazord from "react-native-my-megazord";

const { Crate1Type } = megazord.crate1;
const { Crate2Type } = megazord.crate2;