This demonstrates using cargo container to wrap apps in multiple platforms, displaying a "dialog".

cargo install --path .

cd example\multiplatform
cargo container setup
cargo container build
cargo container test

:: Run the debug platforms\console generated executable
target\debug\alpha.exe

:: Run the debug platforms\windows generated executable
target\x86_64-pc-windows-msvc\debug\alpha.exe

In this example, each "app" (alpha, beta, delta) exposes:

pub fn init(ctx: impl app_common::DialogProvider) { ... }

There is nothing special about this function signature - it only needs to match whatever the accompanying generated packages expect. This might be pub fns, this might be inventory-registered flags... anything!

Each of these generates Cargo.toml [package]s wrapping the aforementioned apps.

Displays the 'dialog' via stdout, waits for response via stdin

fn main() { app::init(app_common::ConsoleDialogProvider) }

Displays the dialog as a javascript alert in the browser, via stdweb.

fn main() { app::init(app_common::StdWebDialogProvider) }

Displays the dialog as a javascript alert in the browser, via web-sys.

#[wasm_bindgen(start)] pub fn start() { app::init(app_common::WebSysDialogProvider) }

Displays the dialog as a message box. Will cross-compile to windows on non-windows platforms.

#![windows_subsystem="windows"] fn main() { app::init(app_common::WindowsDialogProvider) }

In this demo, I abuse traits for monomorphization. Perhaps instead you'd prefer global Mutex<Box<dyn Whatever>>s? This can lead to issues if app uses a different version of app_common. (e.g. reqwest might use tokio 0.2 and explode at runtime because you've only initialized a tokio 0.3 runtime)

fn main() {
    let dp : Box<dyn DialogProvider> = Box::new(ConsoleDialogProvider);
    app_common::set_dialog_provider(dp);
    app::init();
}

Alternatively, maybe you can make app_common entirely self configuring:

fn main() {
    app::init();
}

Multiple entry points for different frontends is also possible:

// Different platform feature-sets?
pub fn init_console(ctx: impl GamepadInput) { ... }
pub fn init_desktop(ctx: impl GamepadInput + KeyboardInput + MouseInput) { ... }

// Different contexts
pub fn render_2d(ctx: impl RenderContext2D) { ... }
pub fn render_3d(ctx: impl RenderContext3D) { ... }