Stateful Rust

What if our Rust code needs to be stateful? Here are some non-exhaustive possibilities using the flutter_rust_bridge features.

Automatic arbitrary Rust types

The automatic arbitrary Rust types can be used to hold the state - just write normal Rust code, and use #[frb(opaque)] on your struct to ensure it is never serialized and transferred across the language boundary.

I personally prefer this approach, because it is the most seamless, and avoid introducing any global variables (we know global variables do not have a very good reputation).

Please refer to gallery demo for some in-action examples.

Alternative: lazy_static

The lazy_static, or any other static variable solution in Rust, can also be used to hold states in Rust. This is a Rust feature and is unrelated to flutter_rust_bridge.

Alternative: Copy data

If the state is quite small, it may also be a choice to transfer the state back and forth between Rust and Dart. This is again automatically done, as long as your struct is recognized as non-opaque.