Gpui Entity

Overview

An Entity<T> is a handle to state of type T, providing safe access and updates.

Key Methods:

• entity.read(cx) → &T - Read-only access
• entity.read_with(cx, |state, cx| ...) → R - Read with closure
• entity.update(cx, |state, cx| ...) → R - Mutable update
• entity.downgrade() → WeakEntity<T> - Create weak reference
• entity.entity_id() → EntityId - Unique identifier

Entity Types:

• Entity<T>: Strong reference (increases ref count)
• WeakEntity<T>: Weak reference (doesn't prevent cleanup, returns Result)

Quick Start

Creating and Using Entities

// Create entity
let counter = cx.new(|cx| Counter { count: 0 });

// Read state
let count = counter.read(cx).count;

// Update state
counter.update(cx, |state, cx| {
    state.count += 1;
    cx.notify(); // Trigger re-render
});

// Weak reference (for closures/callbacks)
let weak = counter.downgrade();
let _ = weak.update(cx, |state, cx| {
    state.count += 1;
    cx.notify();
});

In Components

struct MyComponent {
    shared_state: Entity<SharedData>,
}

impl MyComponent {
    fn new(cx: &mut App) -> Entity<Self> {
        let shared = cx.new(|_| SharedData::default());

        cx.new(|cx| Self {
            shared_state: shared,
        })
    }

    fn update_shared(&mut self, cx: &mut Context<Self>) {
        self.shared_state.update(cx, |state, cx| {
            state.value = 42;
            cx.notify();
        });
    }
}

Async Operations

impl MyComponent {
    fn fetch_data(&mut self, cx: &mut Context<Self>) {
        let weak_self = cx.entity().downgrade();

        cx.spawn(async move |cx| {
            let data = fetch_from_api().await;

            // Update entity safely
            let _ = weak_self.update(cx, |state, cx| {
                state.data = Some(data);
                cx.notify();
            });
        }).detach();
    }
}

Core Principles

Always Use Weak References in Closures

// ✅ Good: Weak reference prevents retain cycles
let weak = cx.entity().downgrade();
callback(move || {
    let _ = weak.update(cx, |state, cx| cx.notify());
});

// ❌ Bad: Strong reference may cause memory leak
let strong = cx.entity();
callback(move || {
    strong.update(cx, |state, cx| cx.notify());
});

Use Inner Context

// ✅ Good: Use inner cx from closure
entity.update(cx, |state, inner_cx| {
    inner_cx.notify(); // Correct
});

// ❌ Bad: Use outer cx (multiple borrow error)
entity.update(cx, |state, inner_cx| {
    cx.notify(); // Wrong!
});

Avoid Nested Updates

// ✅ Good: Sequential updates
entity1.update(cx, |state, cx| { /* ... */ });
entity2.update(cx, |state, cx| { /* ... */ });

// ❌ Bad: Nested updates (may panic)
entity1.update(cx, |_, cx| {
    entity2.update(cx, |_, cx| { /* ... */ });
});

Common Use Cases

1. Component State: Internal state that needs reactivity
2. Shared State: State shared between multiple components
3. Parent-Child: Coordinating between related components (use weak refs)
4. Async State: Managing state that changes from async operations
5. Observations: Reacting to changes in other entities

Reference Documentation

Complete API Documentation

• Entity API: See api-reference.md
  • Entity types, methods, lifecycle
  • Context methods, async operations
  • Error handling, type conversions

Implementation Guides

• Patterns: See patterns.md

  • Model-view separation, state management
  • Cross-entity communication, async operations
  • Observer pattern, event subscription
  • Pattern selection guide

• Best Practices: See best-practices.md

  • Avoiding common pitfalls, memory leaks
  • Performance optimization, batching updates
  • Lifecycle management, cleanup
  • Async best practices, testing

• Advanced Patterns: See advanced.md

  • Entity collections, registry pattern
  • Debounced/throttled updates, state machines
  • Entity snapshots, transactions, pools

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