Exploring Xilem: A Rust‑Based Native UI Framework Inspired by Flutter, SwiftUI, and Elm

In today’s fast‑moving software development landscape, UI frameworks play a crucial role, and Rust is emerging as a language for building high‑performance, reliable UI libraries. Xilem is an experimental Rust native UI framework that blends ideas from Flutter, SwiftUI, and Elm, offering developers a fresh way to construct user interfaces.

Xilem Architecture Overview

Xilem's architecture is built around lightweight view objects, diff‑based updates, strong typing, componentization, memoization, and optional type erasure.

The diagram below shows the overall project structure:

From the diagram, the core of Xilem consists of the xilem_core and Masonry crates. Masonry handles low‑level graphics rendering, window management, text processing, and accessibility, and depends on the following libraries:

winit: window creation

Vello and wgpu: 2D graphics rendering

Parley: text handling

AccessKit: accessibility APIs

Program Flow

Xilem follows a centralized state‑management model similar to Elm. For each UI interaction cycle, the framework invokes a closure with a mutable reference to the application state, which returns a view tree describing the UI. The view tree is short‑lived, used for rendering and event dispatch, then diffed against the next tree.

A simple counter example illustrates this flow:

<code>fn app_logic(data: &amp;mut u32) -> impl View&lt;u32, (), Element = impl Widget&gt; {
    Column::new((
        Button::new(format!("count: {}", data), |data| *data += 1),
        Button::new("reset", |data| *data = 0),
    ))
}
</code>

In this example the state is an integer, and the view tree is a column containing two buttons that modify the state when clicked.

Componentization

Componentization allows UI to be split into independent, reusable modules, similar to React. The following example shows how to define and use a component in Xilem:

<code>struct AppData {
    count: u32,
}

fn count_button(count: u32) -> impl View&lt;u32, (), Element = impl Widget&gt; {
    Button::new(format!("count: {}", count), |data| *data += 1)
}

fn app_logic(data: &amp;mut AppData) -> impl View&lt;AppData, (), Element = impl Widget&gt; {
    Adapt::new(|data: &amp;mut AppData, thunk| thunk.call(&amp;mut data.count),
        count_button(data.count))
}
</code>

Here count_button is a standalone component that receives a number and returns a button displaying the count. The Adapt node passes part of the application state to the child component and handles its callbacks.

Memoization

To improve performance, Xilem supports memoization: when a subtree’s rendering depends only on data that hasn’t changed, the framework reuses the previous rendering result instead of recomputing it.

Example of using memoization:

<code>fn app_logic(data: &amp;mut AppData) -> impl View&lt;AppData, (), Element = impl Widget&gt; {
    Memoize::new(data.count, |count| {
        Button::new(format!("count: {}", count), |data: &amp;mut AppData| {
            data.count += 1
        })
    })
}
</code>

The Memoize node caches the Button rendering; it only re‑renders when data.count changes.

Optional Type Erasure

For flexibility while retaining type safety, Xilem offers optional type erasure. By default view nodes are strongly typed, but this can limit dynamic UI scenarios. Xilem provides an AnyView mechanism, similar to SwiftUI, allowing developers to erase a node’s concrete type when needed.

Conclusion

Xilem is an experimental Rust native UI framework that blends strengths from several leading UI toolkits, offering advanced design concepts, powerful features, and a promising future as it matures within the Rust ecosystem.