Struct Engine 

pub struct Engine { /* private fields */ }

The main Hypen engine that orchestrates reactive UI rendering.

Architecture: Shared Engine, Namespaced State

Multi-module applications share a single Engine instance. Each module registers its state under a lowercase-name prefix (e.g., search) so the engine holds one merged state tree. The SDK layer (HypenModuleInstance in TypeScript, ModuleInstance in Kotlin/Swift/Go) manages module lifecycles, action routing, and cross-module communication – the engine itself only sees a flat JSON state and resolves @{state.xxx} bindings against it.

Multi-module Applications

1. One shared engine – all modules register their namespaced state into it. There is NOT one engine per module.

2. SDK-managed module instances – each SDK maintains multiple module instances (e.g., HypenModuleInstance in TypeScript), each with its own state tracking (Proxy in TS, ObservableState in Kotlin/Swift/Go).

3. Cross-module communication uses HypenGlobalContext:

   // In Search's action handler:
   const app = context.getModule<AppState>("App");
   const currentView = app.getState().currentView;
   app.setState({ showSearch: true });

4. State binding scope: Each module’s template binds to its own state via the namespace prefix. Cross-module data flows through the global context, keeping each module’s reactive graph self-contained.

Design Rationale

Keeping one shared engine avoids duplicating the parser, reconciler, and dependency graph per module. Namespaced state keys ensure modules don’t shadow each other’s fields while the engine’s path-based dependency tracker naturally scopes re-renders to only the affected module’s bindings.

Implementations

impl Engine

pub fn new() -> Self

pub fn register_component(&mut self, component: Component)

Register a custom component

pub fn set_component_resolver<F>(&mut self, resolver: F)

where F: Fn(&str, Option<&str>) -> Option<ResolvedComponent> + Send + Sync + 'static,

Set the component resolver for dynamic component loading The resolver receives (component_name, context_path) and should return ResolvedComponent { source, path } or None

pub fn register_resource(&mut self, name: &str, svg: &str)

Register a single resource from raw SVG content.

pub fn register_resources(&mut self, map: IndexMap<String, String>)

Register multiple resources from a name -> SVG map.

pub fn resource_registry(&self) -> &ResourceRegistry

Get access to the resource registry

pub fn resource_registry_mut(&mut self) -> &mut ResourceRegistry

Get mutable access to the resource registry

pub fn icon_registry(&self) -> &ResourceRegistry

Backwards-compatible alias

pub fn icon_registry_mut(&mut self) -> &mut ResourceRegistry

Backwards-compatible alias

pub fn set_module(&mut self, module: ModuleInstance)

Set the primary module instance (backward-compatible single-module API).

pub fn register_module( &mut self, name: impl Into<String>, module: ModuleInstance, )

Register a named module for multi-module apps.

The engine scopes @{state.xxx} bindings to this module’s state when rendering a component whose source starts with module <name> { ... }. The name should be lowercase (e.g., "search").

Also registers the module’s declared actions in the action->module map so that update_state after dispatch_action automatically routes to the correct module.

pub fn get_module_state(&self, name: &str) -> Option<&Value>

Get a named module’s state (for reconciler lookups).

pub fn modules(&self) -> &IndexMap<String, ModuleInstance>

Get access to all registered modules (for reconciler).

pub fn set_render_callback<F>(&mut self, callback: F)

where F: Fn(&[Patch]) + Send + Sync + 'static,

Set the render callback

pub fn on_action<F>(&mut self, action_name: impl Into<String>, handler: F)

where F: Fn(&Action) + Send + Sync + 'static,

Register an action handler

pub fn render(&mut self, element: &Element)

Render an element tree (initial render or full re-render).

This accepts a flat Element. For sources that use ForEach, When, or If, prefer [render_ir_node] which preserves first-class control flow.

pub fn render_ir_node(&mut self, ir_node: &IRNode)

Render an IRNode tree (initial render or full re-render).

Unlike [render], this accepts an IRNode (from ast_to_ir_node()), which preserves ForEach, When, and If as first-class control-flow nodes. This is the same path used by the WASM engine.

pub fn notify_state_change(&mut self, change: &StateChange)

Handle a state change notification from a host that keeps its own state.

Use this when the host already mutated its own state copy and just wants the engine to invalidate and re-render the affected nodes. Engine-owned state should go through [update_state] / [update_state_sparse] instead.

Uses a revision guard: if the primary module’s state hasn’t changed since the last render, this skips the redundant render. This catches SDK Proxy microtasks re-firing after an explicit update_state already processed the same change.

pub fn update_state(&mut self, scope: Option<&str>, state_patch: Value)

Apply a state patch and re-render affected nodes.

scope selects the target module:

• None → primary module set via set_module
• Some(name) → named module registered via [register_module]

Skips rendering if the patch produces no actual state change.

pub fn update_state_sparse( &mut self, scope: Option<&str>, paths: &[String], values: &Value, )

Apply a sparse state patch (path-value pairs) and re-render affected nodes. See [update_state] for scope semantics.

pub fn dispatch_action(&mut self, action: Action) -> Result<(), EngineError>

Dispatch an action to its registered handler.

pub fn action_scope_for(&self, action_name: &str) -> Option<String>

Look up which named module (by lowercased name) owns a given action.

Returns Some(name) when the action was registered via [register_module]. Returns None for both “primary-module actions” (declared on the module set via [set_module]) and “unknown actions” — in both cases callers should route follow-up update_state calls to the primary slot (scope None), which is the correct default.

Callers that host action handlers outside the engine (e.g., the Rust SDK’s RemoteSession) can use this to route an incoming dispatch to the correct module’s state without having to call dispatch_action.

pub fn revision(&self) -> u64

Get the current revision number

pub fn component_registry(&self) -> &ComponentRegistry

Get access to the component registry

pub fn component_registry_mut(&mut self) -> &mut ComponentRegistry

Get mutable access to the component registry

pub fn resources(&self) -> &ResourceCache

Get access to the resource cache

pub fn resources_mut(&mut self) -> &mut ResourceCache

Get mutable access to the resource cache

pub fn set_context(&mut self, name: &str, data: Value)

Set (or replace) a named data source context.

Registers the provider in the dependency graph (if not already known), stores the data, and re-renders every node bound to @name.*. This is the single entry point for all data source writes – sparse merging (if needed) should happen at the SDK layer before calling this method with the merged object.

Example

engine.set_context("spacetime", json!({
    "message": [{ "id": 1, "text": "Hello" }],
    "user": [{ "id": 1, "name": "Alice" }]
}));

pub fn remove_context(&mut self, name: &str)

Remove a data source context entirely.

Drops the provider’s state and re-renders bound nodes (they resolve to null).

pub fn data_sources(&self) -> &IndexMap<String, Value>

Get read access to the data sources map.

Trait Implementations

impl Default for Engine

fn default() -> Self

Returns the “default value” for a type.