Merge 7b870e8f3c into a703e2c361

README.md

@@ -62,3 +62,32 @@ Can be found under /benches/visual/query.luau
 Inserting 8 components to an entity and updating them over 50 times.
 ![Insertions](assets/image-4.png)
 Can be found under /benches/visual/insertions.luau
+
+## Installation
+
+### Using Wally
+
+Add jecs to your `wally.toml` file:
+
+```toml
+[dependencies]
+jecs = "ukendio/jecs@0.1.0"
+```
+
+Then run `wally install` in your project directory.
+
+### Manual Installation
+
+Download the latest release from the [releases page](https://github.com/ukendio/jecs/releases).
+
+## Documentation
+
+For complete documentation, visit our [documentation site](https://ukendio.github.io/jecs/).
+
+## Contributing
+
+Contributions are welcome. Please feel free to submit a Pull Request.
+
+## License
+
+This project is licensed under the MIT License - see the [LICENSE](LICENSE) file for details.

docs/api/jecs.md

@@ -16,6 +16,12 @@ jecs.Wildcard: Entity
 ```
 Builtin component type. This ID is used for wildcard queries.
 
+## w
+```luau
+jecs.w: Entity
+```
+An alias for `jecs.Wildcard`. This ID is used for wildcard queries, providing a shorter syntax in query operations.
+
 ## Component
 ```luau
 jecs.Component: Entity
@@ -28,6 +34,54 @@ jecs.ChildOf: Entity
 ```
 Builtin component type. This ID is for creating parent-child hierarchies.
 
+## Name
+```luau
+jecs.Name: Entity
+```
+Builtin component type. This ID is used to associate a string name with an entity, typically for debugging or display purposes.
+
+## OnAdd
+```luau
+jecs.OnAdd: Entity<(entity: Entity) -> ()>
+```
+Builtin component hook. When set on a component, the provided function is called whenever that component is added to an entity.
+
+## OnRemove
+```luau
+jecs.OnRemove: Entity<(entity: Entity) -> ()>
+```
+Builtin component hook. When set on a component, the provided function is called whenever that component is removed from an entity.
+
+## OnSet
+```luau
+jecs.OnSet: Entity<(entity: Entity, data: any) -> ()>
+```
+Builtin component hook. When set on a component, the provided function is called whenever that component's value is set or changed on an entity.
+
+## OnDelete
+```luau
+jecs.OnDelete: Entity
+```
+Builtin component trait. Used with `pair()` to define behavior when a component or entity is deleted. Must be paired with an action component like `jecs.Delete` or `jecs.Remove`.
+
+## OnDeleteTarget
+```luau
+jecs.OnDeleteTarget: Entity
+```
+Builtin component trait. Used with `pair()` to define behavior when a relationship target is deleted. Must be paired with an action component like `jecs.Delete` or `jecs.Remove`.
+
+## Delete
+```luau
+jecs.Delete: Entity
+```
+Builtin action component used with `OnDelete` or `OnDeleteTarget` to specify that entities should be deleted in the cleanup process.
+
+## Remove
+```luau
+jecs.Remove: Entity
+```
+Builtin action component used with `OnDelete` or `OnDeleteTarget` to specify that components should be removed in the cleanup process.
+
 ## Rest
 ```luau
 jecs.Rest: Entity

docs/api/name.md

@@ -0,0 +1,130 @@
+# Name Component
+
+The `Name` component allows you to associate a string identifier with an entity.
+
+## Overview
+
+```luau
+jecs.Name: Entity<string>
+```
+
+The `Name` component is a built-in component in jecs that stores a string value. It has no special behavior beyond storing a name.
+
+## Usage
+
+### Setting a Name
+
+```luau
+local world = jecs.World.new()
+
+-- Create an entity
+local entity = world:entity()
+
+-- Assign a name to the entity
+world:set(entity, jecs.Name, "Player")
+```
+
+### Getting an Entity's Name
+
+```luau
+-- Retrieve an entity's name
+local name = world:get(entity, jecs.Name)
+print("Entity name:", name) -- Outputs: "Entity name: Player"
+```
+
+### Finding Entities by Name
+
+```luau
+-- Iterate over all entities with the Name component
+for entity, name in world:query(jecs.Name) do
+  if name == "Player" then
+    -- Found the entity named "Player"
+    -- Do something with entity...
+  end
+end
+```
+
+### Using Names with Hierarchies
+
+Names are particularly useful when working with entity hierarchies:
+
+```luau
+local world = jecs.World.new()
+local pair = jecs.pair
+
+-- Create a parent entity with a name
+local parent = world:entity()
+world:set(parent, jecs.Name, "Parent")
+
+-- Create child entities with names
+local child1 = world:entity()
+world:set(child1, jecs.Name, "Child1")
+world:add(child1, pair(jecs.ChildOf, parent))
+
+local child2 = world:entity()
+world:set(child2, jecs.Name, "Child2")
+world:add(child2, pair(jecs.ChildOf, parent))
+
+-- Print the hierarchy
+print("Parent:", world:get(parent, jecs.Name))
+for child in world:query(pair(jecs.ChildOf, parent)) do
+  print("  Child:", world:get(child, jecs.Name))
+end
+
+-- Output:
+-- Parent: Parent
+--   Child: Child1
+--   Child: Child2
+```
+
+## Helper Function
+
+For convenience, you can create a simple helper function to get an entity's name:
+
+```luau
+local function getName(world, entity)
+  return world:get(entity, jecs.Name) or tostring(entity)
+end
+
+-- Usage
+local name = getName(world, entity)
+```
+
+This function will return the entity's name if it has one, or fall back to the entity ID as a string.
+
+## Best Practices
+
+1. **Use Consistently**: Apply names to key entities systematically, especially for important game objects.
+
+2. **Be Descriptive**: Use meaningful names that describe the entity's role or purpose.
+
+3. **Handle Missing Names**: Always check if an entity has a name before trying to use it, or use a helper function like the one above.
+
+4. **Namespacing**: Consider using prefixes or namespaces for different systems (e.g., "UI:MainMenu", "Enemy:Boss").
+
+5. **Performance**: Remember that adding a Name component to every entity adds memory overhead. Use judiciously in performance-critical applications.
+
+## Example: Entity Debugging System
+
+Here's a simple debugging system that uses the Name component:
+
+```luau
+local function debugEntity(world, entity)
+  local name = world:get(entity, jecs.Name) or "Unnamed"
+  print("Entity", entity, "(" .. name .. ")")
+  
+  -- Print all components
+  for componentId in world:query(jecs.pair(jecs.Component, jecs.Wildcard)) do
+    if world:has(entity, componentId) then
+      local componentName = world:get(componentId, jecs.Name) or "Unknown"
+      local value = world:get(entity, componentId)
+      print("  Component:", componentName, "=", value)
+    end
+  end
+end
+
+-- Usage
+debugEntity(world, player)
+```
+
+This debugging function prints an entity's name along with all its components, making it easier to inspect entities during development. 

docs/api/world-entity-management.md

@@ -0,0 +1,215 @@
+# Entity Management
+
+This section covers methods for managing entities in the jecs World.
+
+## delete
+
+Deletes an entity (and its components/relationships) from the world entirely.
+
+```luau
+function World:delete(entity: Entity): void
+```
+
+### Parameters
+
+| Name | Type | Description |
+|------|------|-------------|
+| entity | Entity | The entity to delete from the world |
+
+### Behavior
+
+1. Invokes any `OnRemove` hooks for all components on the entity
+2. Triggers any cleanup actions based on `OnDelete` and `OnDeleteTarget` relationships
+3. Removes the entity from all archetypes
+4. Recycles the entity ID for future use
+
+### Example
+
+::: code-group
+
+```luau [luau]
+local world = jecs.World.new()
+
+-- Create an entity
+local entity = world:entity()
+world:set(entity, Position, {x = 0, y = 0})
+
+-- Delete the entity
+world:delete(entity)
+
+-- The entity no longer exists in the world
+assert(not world:contains(entity))
+```
+
+```typescript [typescript]
+import { World } from "@rbxts/jecs";
+
+const world = new World();
+
+// Create an entity
+const entity = world.entity();
+world.set(entity, Position, {x: 0, y: 0});
+
+// Delete the entity
+world.delete(entity);
+
+// The entity no longer exists in the world
+assert(!world.contains(entity));
+```
+
+:::
+
+### Child Entity Deletion
+
+When an entity has children (via the `ChildOf` relationship), deleting the parent can also delete the children if the appropriate cleanup policy is set:
+
+```luau
+-- Set up parent-child relationship
+local ChildOf = world:component()
+world:add(ChildOf, jecs.pair(jecs.OnDeleteTarget, jecs.Delete))
+
+local parent = world:entity()
+local child = world:entity()
+
+-- Make child a child of parent
+world:add(child, jecs.pair(ChildOf, parent))
+
+-- Deleting parent will also delete child
+world:delete(parent)
+assert(not world:contains(child))
+```
+
+### Component Deletion
+
+The `delete` method can also be used to delete a component definition:
+
+```luau
+local Temporary = world:component()
+world:add(Temporary, jecs.pair(jecs.OnDelete, jecs.Remove))
+
+-- Add Temporary to entities
+local e1 = world:entity()
+local e2 = world:entity()
+world:add(e1, Temporary)
+world:add(e2, Temporary)
+
+-- Delete the component definition
+world:delete(Temporary)
+
+-- Temporary is removed from all entities
+assert(not world:has(e1, Temporary))
+assert(not world:has(e2, Temporary))
+```
+
+## remove
+
+Removes a component from a given entity.
+
+```luau
+function World:remove(entity: Entity, component: Id): void
+```
+
+### Parameters
+
+| Name | Type | Description |
+|------|------|-------------|
+| entity | Entity | The entity to modify |
+| component | Id | The component or relationship to remove |
+
+### Behavior
+
+1. Invokes any `OnRemove` hook for the component being removed
+2. Removes the component from the entity
+3. May cause the entity to transition to another archetype
+
+### Example
+
+::: code-group
+
+```luau [luau]
+local world = jecs.World.new()
+
+-- Create components
+local Health = world:component()
+local Shield = world:component()
+
+-- Create an entity with both components
+local entity = world:entity()
+world:set(entity, Health, 100)
+world:set(entity, Shield, 50)
+
+-- Remove just the Shield component
+world:remove(entity, Shield)
+
+-- Entity still exists but no longer has Shield
+assert(world:contains(entity))
+assert(world:has(entity, Health))
+assert(not world:has(entity, Shield))
+```
+
+```typescript [typescript]
+import { World } from "@rbxts/jecs";
+
+const world = new World();
+
+// Create components
+const Health = world.component();
+const Shield = world.component();
+
+// Create an entity with both components
+const entity = world.entity();
+world.set(entity, Health, 100);
+world.set(entity, Shield, 50);
+
+// Remove just the Shield component
+world.remove(entity, Shield);
+
+// Entity still exists but no longer has Shield
+assert(world.contains(entity));
+assert(world.has(entity, Health));
+assert(!world.has(entity, Shield));
+```
+
+:::
+
+### Removing Relationships
+
+The `remove` method can also be used to remove relationship pairs:
+
+```luau
+local ChildOf = world:component()
+local parent = world:entity()
+local child = world:entity()
+
+-- Establish parent-child relationship
+world:add(child, jecs.pair(ChildOf, parent))
+
+-- Remove the relationship
+world:remove(child, jecs.pair(ChildOf, parent))
+
+-- Child is no longer related to parent
+assert(not world:has(child, jecs.pair(ChildOf, parent)))
+```
+
+## Differences Between delete and remove
+
+| Method | What It Affects | Entity Existence | Cleanup Policies |
+|--------|-----------------|------------------|------------------|
+| delete | Entity and all its components | Entity no longer exists | Triggers all cleanup policies |
+| remove | Only the specified component | Entity still exists | Only triggers component-specific OnRemove hook |
+
+### When to Use Each Method
+
+- Use `delete` when you want to completely remove an entity from the world
+- Use `remove` when you want to keep the entity but remove specific components
+- Use `delete` on a component definition to remove that component from all entities
+
+### Performance Considerations
+
+Both operations may cause archetype transitions, which have performance implications:
+
+- `delete` typically has more overhead because it has to remove all components
+- `remove` is generally faster for individual component removal
+- Both methods are optimized in jecs to be as efficient as possible
+
+For performance-critical code dealing with many entities, consider batching operations to minimize archetype transitions. 

docs/learn/faq/contributing.md

@@ -1,3 +1,84 @@
-## TODO
+# Contributing to jecs
 
-This is a TODO stub.
+This document provides guidelines for contributing to the project.
+
+## Getting Started
+
+1. Fork the repository
+2. Clone your fork
+3. Set up the development environment
+4. Create a branch for your changes
+
+## Development Setup
+
+```bash
+# Clone your fork
+git clone https://github.com/your-username/jecs.git
+cd jecs
+
+# Install dependencies
+wally install
+```
+
+## Making Changes
+
+1. Create a branch:
+   ```bash
+   git checkout -b feature/your-feature-name
+   ```
+
+2. Make your changes
+
+3. Add tests if applicable
+
+4. Run tests:
+   ```bash
+   lune run test
+   ```
+
+5. Commit your changes:
+   ```bash
+   git commit -m "Add feature: description"
+   ```
+
+## Submitting Changes
+
+1. Push your changes:
+   ```bash
+   git push origin feature/your-feature-name
+   ```
+
+2. Create a Pull Request
+
+3. Explain the changes and reference related issues
+
+## Code Style
+
+- Follow the existing code style
+- Use meaningful variable and function names
+- Write clear comments for complex logic
+- Keep functions focused on a single responsibility
+
+## Testing
+
+- Add tests for new features
+- Ensure all tests pass before submitting
+- Consider edge cases
+
+## Documentation
+
+- Update documentation for changed functionality
+- Document new features or APIs
+- Use clear and concise language
+
+## Issue Reporting
+
+1. Check if the issue already exists in the [Issues](https://github.com/ukendio/jecs/issues) section
+2. Create a new issue with a descriptive title and detailed information
+
+## Code of Conduct
+
+- Be respectful in communications
+- Provide constructive feedback
+- Accept constructive criticism
+- Focus on what is best for the community

docs/learn/faq/index.md

@@ -0,0 +1,94 @@
+# Frequently Asked Questions
+
+This section addresses common questions about jecs.
+
+## General Questions
+
+### What is jecs?
+
+jecs is a high-performance Entity Component System (ECS) library for Luau/Roblox.
+
+### How does jecs compare to other ECS libraries?
+
+jecs uses an archetype-based storage system (SoA) which is more cache-friendly than traditional approaches. For a detailed comparison with Matter, see the [Migration from Matter](../migration-from-matter.md) guide.
+
+### Can I use jecs outside of Roblox?
+
+Yes, jecs can be used in any Lua/Luau environment as it has zero dependencies.
+
+## Technical Questions
+
+### How many entities can jecs handle?
+
+jecs can handle up to 800,000 entities at 60 frames per second.
+
+### What are archetypes?
+
+Archetypes are groups of entities that have the exact same set of components. When you add or remove components from an entity, it moves to a different archetype.
+
+### How do I optimize performance with jecs?
+
+- Group entity operations to minimize archetype transitions
+- Use cached queries for frequently accessed data
+- Define components that are frequently queried together
+- Use tags instead of empty tables
+- Be mindful of archetype transitions
+
+### What are relationship pairs?
+
+Relationship pairs allow you to create connections between entities using the `pair()` function.
+
+## Common Issues
+
+### My entity disappeared after adding a component
+
+Check if you have cleanup policies set up with `OnDelete` or `OnDeleteTarget`.
+
+### Queries are returning unexpected results
+
+Make sure you're querying for the exact components you need. Use modifiers like `.with()` or `.without()` to refine queries.
+
+### Performance degrades over time
+
+This could be due to:
+- Memory leaks from not properly deleting entities
+- Excessive archetype transitions
+- Too many entities or components
+- Inefficient queries
+
+### How do I debug entity relationships?
+
+Use the `Name` component to give entities meaningful names:
+
+```lua
+-- Print all parent-child relationships
+for entity, target in world:query(jecs.pair(jecs.ChildOf, jecs.Wildcard)) do
+  print(world:get(entity, jecs.Name), "is a child of", world:get(target, jecs.Name))
+end
+```
+
+## Best Practices
+
+### When should I use component lifecycle hooks?
+
+Use lifecycle hooks (`OnAdd`, `OnRemove`, `OnSet`) for:
+- Initializing resources
+- Cleaning up resources
+- Reacting to data changes
+
+### How should I structure my ECS code?
+
+- Separate data (components) from behavior (systems)
+- Keep components small and focused
+- Design systems for specific component combinations
+- Use relationships to model connections
+- Document cleanup policies
+
+### Should I use multiple worlds?
+
+Multiple worlds are useful for:
+- Separating client and server logic
+- Creating isolated test environments
+- Managing different game states
+
+Component IDs may conflict between worlds if not registered in the same order. 

docs/learn/migration-from-matter.md

@@ -0,0 +1,218 @@
+# Migrating from Matter to jecs
+
+This guide is intended to help developers migrate from the Matter ECS library to jecs.
+
+## Key Differences
+
+### Architectural Differences
+
+- **Storage Implementation**: jecs uses an archetype-based storage system (SoA - Structure of Arrays). Matter uses a simpler component-based storage approach.
+- **Performance**: jecs is designed with a focus on performance, particularly for large-scale systems with hundreds of thousands of entities.
+- **Relationship Model**: jecs treats entity relationships as first-class citizens. Matter doesn't have built-in relationship features.
+- **Memory Usage**: jecs typically uses less memory for the same number of entities and components due to its optimized storage structure.
+
+### API Differences
+
+#### World Creation and Management
+
+**Matter:**
+```lua
+local Matter = require("Matter")
+local world = Matter.World.new()
+```
+
+**jecs:**
+```lua
+local jecs = require("jecs")
+local world = jecs.World.new()
+```
+
+#### Component Definition
+
+**Matter:**
+```lua
+local Position = Matter.component("Position")
+local Velocity = Matter.component("Velocity") 
+```
+
+**jecs:**
+```lua
+local Position = world:component()
+local Velocity = world:component()
+```
+
+#### Entity Creation
+
+**Matter:**
+```lua
+local entity = world:spawn(
+  Position({x = 0, y = 0}),
+  Velocity({x = 10, y = 5})
+)
+```
+
+**jecs:**
+```lua
+local entity = world:entity()
+world:set(entity, Position, {x = 0, y = 0})
+world:set(entity, Velocity, {x = 10, y = 5})
+```
+
+#### Queries
+
+**Matter:**
+```lua
+for id, position, velocity in world:query(Position, Velocity) do
+  -- Update position based on velocity
+  position.x = position.x + velocity.x * dt
+  position.y = position.y + velocity.y * dt
+end
+```
+
+**jecs:**
+```lua
+for entity, position, velocity in world:query(Position, Velocity) do
+  -- Update position based on velocity
+  position.x = position.x + velocity.x * dt
+  position.y = position.y + velocity.y * dt
+end
+```
+
+#### System Definition
+
+**Matter:**
+```lua
+local function movementSystem(world)
+  for id, position, velocity in world:query(Position, Velocity) do
+    position.x = position.x + velocity.x * dt
+    position.y = position.y + velocity.y * dt
+  end
+end
+```
+
+**jecs:**
+```lua
+local function movementSystem(world, dt)
+  for entity, position, velocity in world:query(Position, Velocity) do
+    position.x = position.x + velocity.x * dt
+    position.y = position.y + velocity.y * dt
+  end
+end
+```
+
+#### Entity Removal
+
+**Matter:**
+```lua
+world:despawn(entity)
+```
+
+**jecs:**
+```lua
+world:delete(entity)
+```
+
+#### Component Removal
+
+**Matter:**
+```lua
+world:remove(entity, Position)
+```
+
+**jecs:**
+```lua
+world:remove(entity, Position)
+```
+
+### jecs-Specific Features
+
+#### Relationships
+
+jecs has built-in support for entity relationships:
+
+```lua
+local ChildOf = world:component()
+local Name = world:component()
+
+local parent = world:entity()
+world:set(parent, Name, "Parent")
+
+local child = world:entity()
+world:add(child, jecs.pair(ChildOf, parent))
+world:set(child, Name, "Child")
+
+-- Query for all children of parent
+for e in world:query(jecs.pair(ChildOf, parent)) do
+  local name = world:get(e, Name)
+  print(name, "is a child of Parent")
+end
+```
+
+#### Wildcards
+
+jecs supports wildcard queries for relationships:
+
+```lua
+-- Query for all parent-child relationships
+for entity, target in world:query(jecs.pair(ChildOf, jecs.Wildcard)) do
+  print(world:get(entity, Name), "is a child of", world:get(target, Name))
+end
+
+-- Alternative using the shorter 'w' alias
+for entity, target in world:query(jecs.pair(ChildOf, jecs.w)) do
+  print(world:get(entity, Name), "is a child of", world:get(target, Name))
+end
+```
+
+#### Observer Hooks
+
+jecs provides component lifecycle hooks:
+
+```lua
+world:set(Position, jecs.OnAdd, function(entity)
+  print("Position added to entity", entity)
+end)
+
+world:set(Position, jecs.OnRemove, function(entity)
+  print("Position removed from entity", entity)
+end)
+
+world:set(Position, jecs.OnSet, function(entity, value)
+  print("Position set on entity", entity, "with value", value)
+end)
+```
+
+#### Automatic Cleanup with OnDelete and OnDeleteTarget
+
+jecs offers automated cleanup of related entities:
+
+```lua
+-- When a parent is deleted, all its children will be deleted too
+world:add(ChildOf, jecs.pair(jecs.OnDeleteTarget, jecs.Delete))
+
+-- When Health component is deleted, remove the entity's Shield component
+world:add(Health, jecs.pair(jecs.OnDelete, jecs.Remove))
+world:add(Shield, jecs.pair(jecs.OnDelete, jecs.Remove))
+```
+
+## Performance Considerations
+
+When migrating from Matter to jecs, consider these performance tips:
+
+1. **Batch Entity Operations**: Group entity operations when possible to minimize archetype transitions.
+2. **Use Cached Queries**: For frequently used queries, create cached versions.
+3. **Consider Component Layout**: Components frequently queried together should be defined together.
+4. **Use Tags When Appropriate**: For components with no data, use tags instead of empty tables.
+5. **Be Aware of Archetype Transitions**: Adding/removing components causes archetype transitions, which have performance implications for large-scale operations.
+
+## Migration Strategy
+
+1. **Start with World Creation**: Replace Matter's world creation with jecs.
+2. **Migrate Component Definitions**: Update component definitions to use jecs's approach.
+3. **Update Entity Creation**: Modify entity spawning code to use jecs's entity and set methods.
+4. **Adapt Queries**: Update queries, noting that iteration patterns are similar.
+5. **Implement Relationships**: Take advantage of jecs's relationship features where applicable.
+6. **Add Observer Hooks**: Implement lifecycle hooks to replace custom event handling in Matter.
+7. **Optimize**: Refine your implementation using jecs-specific features for better performance.
+
+By following this guide, you should be able to migrate your Matter ECS application to jecs while taking advantage of jecs's enhanced performance and features. 

docs/learn/observers.md

@@ -0,0 +1,246 @@
+# Observer APIs
+
+jecs provides observer hooks that allow you to respond to component lifecycle events and implement cleanup policies.
+
+## Component Lifecycle Hooks
+
+Component lifecycle hooks let you execute code when components are added, removed, or modified.
+
+### OnAdd
+
+The `OnAdd` hook is called when a component is added to an entity.
+
+```lua
+-- Define a component
+local Transform = world:component()
+
+-- Set an OnAdd hook for the Transform component
+world:set(Transform, jecs.OnAdd, function(entity)
+  print("Transform component added to entity", entity)
+end)
+
+-- The hook will be called when Transform is added to any entity
+local entity = world:entity()
+world:add(entity, Transform) -- OnAdd hook is triggered
+```
+
+TypeScript signature:
+```typescript
+type OnAddHook = (entity: Entity) => void;
+```
+
+### OnRemove
+
+The `OnRemove` hook is called when a component is removed from an entity.
+
+```lua
+-- Set an OnRemove hook for the Transform component
+world:set(Transform, jecs.OnRemove, function(entity)
+  print("Transform component removed from entity", entity)
+end)
+
+-- The hook will be called when Transform is removed from any entity
+world:remove(entity, Transform) -- OnRemove hook is triggered
+```
+
+TypeScript signature:
+```typescript
+type OnRemoveHook = (entity: Entity) => void;
+```
+
+### OnSet
+
+The `OnSet` hook is called when a component's value is set or changed on an entity.
+
+```lua
+-- Set an OnSet hook for the Transform component
+world:set(Transform, jecs.OnSet, function(entity, value)
+  print("Transform component set on entity", entity, "with value", value)
+end)
+
+-- The hook will be called when Transform's value is set on any entity
+world:set(entity, Transform, { position = {x = 10, y = 20} }) -- OnSet hook is triggered
+```
+
+TypeScript signature:
+```typescript
+type OnSetHook<T> = (entity: Entity, value: T) => void;
+```
+
+## Automatic Cleanup Policies
+
+jecs provides automatic cleanup policies through the `OnDelete` and `OnDeleteTarget` hooks paired with action components.
+
+### OnDelete
+
+The `OnDelete` trait specifies what happens when a component or entity is deleted. It must be paired with an action component like `Delete` or `Remove`.
+
+#### (OnDelete, Delete)
+
+When paired with `Delete`, this policy deletes entities that have the component when the component itself is deleted.
+
+```lua
+-- Define a component
+local Health = world:component()
+
+-- Add the (OnDelete, Delete) cleanup policy to Health
+world:add(Health, jecs.pair(jecs.OnDelete, jecs.Delete))
+
+-- Create entities
+local entity1 = world:entity()
+local entity2 = world:entity()
+
+-- Add Health component to entities
+world:add(entity1, Health)
+world:add(entity2, Health)
+
+-- When Health component is deleted, all entities with Health will be deleted
+world:delete(Health) -- Deletes entity1 and entity2
+```
+
+#### (OnDelete, Remove)
+
+When paired with `Remove`, this policy removes a component from entities when the component itself is deleted.
+
+```lua
+-- Define components
+local Poison = world:component()
+local PoisonEffect = world:component()
+
+-- Add the (OnDelete, Remove) cleanup policy to Poison
+world:add(Poison, jecs.pair(jecs.OnDelete, jecs.Remove))
+world:add(PoisonEffect, jecs.pair(jecs.OnDelete, jecs.Remove))
+
+-- Create entity
+local entity = world:entity()
+world:add(entity, Poison)
+world:add(entity, PoisonEffect)
+
+-- When Poison component is deleted, PoisonEffect will be removed from all entities
+world:delete(Poison) -- Removes PoisonEffect from entity
+```
+
+### OnDeleteTarget
+
+The `OnDeleteTarget` trait specifies what happens when a relationship target is deleted. It must be paired with an action component like `Delete` or `Remove`.
+
+#### (OnDeleteTarget, Delete)
+
+When paired with `Delete`, this policy deletes entities that have a relationship with the deleted target.
+
+```lua
+-- Define a ChildOf component for parent-child relationships
+local ChildOf = world:component()
+
+-- Add the (OnDeleteTarget, Delete) cleanup policy
+world:add(ChildOf, jecs.pair(jecs.OnDeleteTarget, jecs.Delete))
+
+-- Create parent and child entities
+local parent = world:entity()
+local child1 = world:entity()
+local child2 = world:entity()
+
+-- Establish parent-child relationships
+world:add(child1, jecs.pair(ChildOf, parent))
+world:add(child2, jecs.pair(ChildOf, parent))
+
+-- When the parent is deleted, all its children will be deleted too
+world:delete(parent) -- Deletes child1 and child2
+```
+
+#### (OnDeleteTarget, Remove)
+
+When paired with `Remove`, this policy removes a relationship component when its target is deleted.
+
+```lua
+-- Define a Likes component for relationships
+local Likes = world:component()
+
+-- Add the (OnDeleteTarget, Remove) cleanup policy
+world:add(Likes, jecs.pair(jecs.OnDeleteTarget, jecs.Remove))
+
+-- Create entities
+local bob = world:entity()
+local alice = world:entity()
+local charlie = world:entity()
+
+-- Establish relationships
+world:add(bob, jecs.pair(Likes, alice))
+world:add(charlie, jecs.pair(Likes, alice))
+
+-- When alice is deleted, all Likes relationships targeting her will be removed
+world:delete(alice) -- Removes Likes relationship from bob and charlie
+```
+
+## Best Practices
+
+1. **Use hooks for reactive logic**: Component hooks are perfect for synchronizing game state with visual representations or external systems.
+
+2. **Keep hook logic simple**: Hooks should be lightweight and focused on a single concern.
+
+3. **Consider cleanup policies carefully**: The right cleanup policies can prevent memory leaks and simplify your codebase by automating entity management.
+
+4. **Avoid infinite loops**: Be careful not to create circular dependencies with your hooks and cleanup policies.
+
+5. **Document your policies**: When using cleanup policies, document them clearly so other developers understand the entity lifecycle in your application.
+
+6. **Use OnAdd for initialization**: The OnAdd hook is ideal for initializing component-specific resources.
+
+7. **Use OnRemove for cleanup**: The OnRemove hook ensures resources are properly released when components are removed.
+
+8. **Use OnSet for synchronization**: The OnSet hook helps keep different aspects of your game in sync when component values change.
+
+## Example: Complete Entity Lifecycle
+
+This example shows how to use all observer hooks together to manage an entity's lifecycle:
+
+```lua
+local world = jecs.World.new()
+local pair = jecs.pair
+
+-- Define components
+local Model = world:component()
+local Transform = world:component()
+local ChildOf = world:component()
+
+-- Set up component hooks
+world:set(Model, jecs.OnAdd, function(entity)
+    print("Model added to entity", entity)
+    -- Create visual representation
+end)
+
+world:set(Model, jecs.OnRemove, function(entity)
+    print("Model removed from entity", entity)
+    -- Destroy visual representation
+end)
+
+world:set(Model, jecs.OnSet, function(entity, model)
+    print("Model set on entity", entity, "with value", model)
+    -- Update visual representation
+end)
+
+-- Set up cleanup policies
+world:add(ChildOf, pair(jecs.OnDeleteTarget, jecs.Delete))
+world:add(Transform, pair(jecs.OnDelete, jecs.Remove))
+
+-- Create entities
+local parent = world:entity()
+local child = world:entity()
+
+-- Set up relationships and components
+world:add(child, pair(ChildOf, parent))
+world:set(child, Model, "cube")
+world:set(child, Transform, {position = {x = 0, y = 0, z = 0}})
+
+-- Updating a component triggers the OnSet hook
+world:set(child, Model, "sphere")
+
+-- Removing a component triggers the OnRemove hook
+world:remove(child, Model)
+
+-- Deleting the parent triggers the OnDeleteTarget cleanup policy
+-- which automatically deletes the child
+world:delete(parent)
+```
+
+By effectively using observer hooks and cleanup policies, you can create more maintainable and robust ECS-based applications with less manual resource management. 

jecs.luau

@@ -172,9 +172,6 @@ end
 
 local function entity_index_try_get_any(entity_index: EntityIndex, entity: number): Record?
 	local r = entity_index.sparse_array[ECS_ENTITY_T_LO(entity)]
-	if not r then
-		return nil
-	end
 
 	if not r or r.dense == 0 then
 		return nil

mkdocs.yml

@@ -51,8 +51,64 @@ extra_css:
 extra_javascript:
   - assets/scripts/smooth-scroll.js
 
+plugins:
+  - search
+  - mike:
+      version_selector: true
+      canonical_version: latest
+  - mkdocstrings:
+      default_handler: python
+      handlers:
+        python:
+          import:
+            - https://installer.github.io/docs/python-objects.inv
+            - https://docs.python.org/3/objects.inv
+          selection:
+            members: true
+          rendering:
+            show_source: true
+            show_submodules: true
+          paths: [src]
+
 nav:
   - Home: index.md
+  - Learn:
+    - learn/index.md
+    - Getting Started:
+      - Installation: learn/getting-started/installation.md
+      - Quick start: learn/getting-started/quick-start.md
+    - Concepts:
+      - Entities & Components: learn/concepts/entities-components.md
+      - Queries: learn/concepts/queries.md
+      - Component Traits: learn/concepts/component-traits.md
+      - Command line: learn/concepts/command-line.md
+      - Addons: learn/concepts/addons.md
+    - Guides:
+      - learn/guides/index.md
+      - Hello, World: learn/guides/hello-world.md
+      - Reading Queries: learn/guides/reading-queries.md
+      - Pair Rules: learn/guides/pair-rules.md
+      - Tagging: learn/guides/tagging.md
+      - Removing Components: learn/guides/removing-components.md
+      - Bulk Operations: learn/guides/bulk.md
+      - Bulk Queries: learn/guides/bulk-queries.md
+      - Debugging: learn/guides/debugging.md
+      - Naming: learn/guides/naming.md
+      - Building Applications: learn/guides/building-applications.md
+      - Troubleshoot: learn/guides/troubleshoot.md
+    - Migration from Matter: learn/migration-from-matter.md
+    - Observer APIs: learn/observers.md
+    - FAQ: learn/faq/index.md
+  - API:
+    - api/jecs.md
+    - World: api/world.md
+    - Query: api/query.md
+    - Entity Management: api/world-entity-management.md 
+    - Name Component: api/name.md
+  - Contributing:
+    - contributing/index.md
+    - Roadmap: contributing/roadmap.md
+    - How to Contribute: learn/faq/contributing.md
   - Tutorials:
     - Get Started: tutorials/index.md
     - Installing Fusion: tutorials/get-started/installing-fusion.md