Struct CowState 

pub struct CowState<S: State> { /* private fields */ }

Copy-on-write state wrapper (default state wrapper)

For large states (e.g., long conversation histories), cloning the entire state for each node spawn is expensive. CowState uses Arc to share immutable state and only clones when modified.

This is the DEFAULT state wrapper in Juncture, not just an optimization.

Implementations

impl<S: State> CowState<S>

pub const fn new(state: Arc<S>) -> Self

Create CowState from shared state

pub fn get(&self) -> &S

Get current state (read-only)

pub fn get_mut(&mut self) -> &mut S

where S: Clone,

Get mutable access to the state, cloning the inner Arc if shared

Uses clone-on-write semantics: if the Arc reference count is greater than one, the inner state is cloned before returning a mutable reference. This ensures no other CowState instances are affected by mutations.

pub fn update(&mut self, changes: S::Update)

Apply an update (deferred until commit)

Note: For proper merge semantics, this implementation simply stores the latest update. The proc-macro generates more sophisticated merge logic for complex update types.

pub fn commit(self) -> Arc<S>

Commit updates and return new shared state

pub fn try_commit(self) -> Result<Arc<S>, InvalidUpdateError>

Commit updates and return new shared state, propagating reducer errors

Unlike commit(), this method returns a structured error when reducer constraints are violated (e.g., multiple writers on a replace channel).

Errors

Returns InvalidUpdateError if the update violates reducer constraints.

Trait Implementations

impl<S: State> Clone for CowState<S>

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<S: Debug + State> Debug for CowState<S>

where S::Update: Debug,

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<S: State> Deref for CowState<S>

type Target = S

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.