impl Global for AppSettings {}


### Set and Access Globals

```rust
fn main() {
    let app = Application::new();
    app.run(|cx: &mut App| {
        // Set global
        cx.set_global(AppSettings {
            theme: Theme::Dark,
            language: "en".to_string(),
        });

        // Access global (read-only)
        let settings = cx.global::<AppSettings>();
        println!("Theme: {:?}", settings.theme);
    });
}

Update Globals

impl MyComponent {
    fn change_theme(&mut self, new_theme: Theme, cx: &mut Context<Self>) {
        cx.update_global::<AppSettings, _>(|settings, cx| {
            settings.theme = new_theme;
            // Global updates don't trigger automatic notifications
            // Manually notify components that care
        });

        cx.notify(); // Re-render this component
    }
}

Common Use Cases

1. App Configuration

#[derive(Clone)]
struct AppConfig {
    api_endpoint: String,
    max_retries: u32,
    timeout: Duration,
}

impl Global for AppConfig {}

// Set once at startup
cx.set_global(AppConfig {
    api_endpoint: "https://api.example.com".to_string(),
    max_retries: 3,
    timeout: Duration::from_secs(30),
});

// Access anywhere
let config = cx.global::<AppConfig>();

2. Feature Flags

#[derive(Clone)]
struct FeatureFlags {
    enable_beta_features: bool,
    enable_analytics: bool,
}

impl Global for FeatureFlags {}

impl MyComponent {
    fn render_beta_feature(&self, cx: &App) -> Option<impl IntoElement> {
        let flags = cx.global::<FeatureFlags>();

        if flags.enable_beta_features {
            Some(div().child("Beta feature"))
        } else {
            None
        }
    }
}

3. Shared Services

#[derive(Clone)]
struct ServiceRegistry {
    http_client: Arc<HttpClient>,
    logger: Arc<Logger>,
}

impl Global for ServiceRegistry {}

impl MyComponent {
    fn fetch_data(&mut self, cx: &mut Context<Self>) {
        let registry = cx.global::<ServiceRegistry>();
        let client = registry.http_client.clone();

        cx.spawn(async move |cx| {
            let data = client.get("api/data").await?;
            // Process data...
            Ok::<_, anyhow::Error>(())
        }).detach();
    }
}

Best Practices

✅ Use Arc for Shared Resources

#[derive(Clone)]
struct GlobalState {
    database: Arc<Database>,  // Cheap to clone
    cache: Arc<RwLock<Cache>>,
}

impl Global for GlobalState {}

✅ Immutable by Default

Globals are read-only by default. Use interior mutability when needed:

#[derive(Clone)]
struct Counter {
    count: Arc<AtomicUsize>,
}

impl Global for Counter {}

impl Counter {
    fn increment(&self) {
        self.count.fetch_add(1, Ordering::SeqCst);
    }

    fn get(&self) -> usize {
        self.count.load(Ordering::SeqCst)
    }
}

❌ Don't: Overuse Globals

// ❌ Bad: Too many globals
cx.set_global(UserState { ... });
cx.set_global(CartState { ... });
cx.set_global(CheckoutState { ... });

// ✅ Good: Use entities for component state
let user_entity = cx.new(|_| UserState { ... });

When to Use

Use Globals for:

App-wide configuration
Feature flags
Shared services (HTTP client, logger)
Read-only reference data

Use Entities for:

Component-specific state
State that changes frequently
State that needs notifications

Reference Documentation

API Reference: See api-reference.md
- Global trait, set_global, update_global
- Interior mutability patterns
- Best practices and anti-patterns

gpui-global

Overview

Quick Start

Define Global State

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