Enum ProtocolAnnotation 

pub enum ProtocolAnnotation {
    TimedChoice {
        duration: Duration,
    },
    Priority(u32),
    Retry {
        max_attempts: u32,
        delay: Option<Duration>,
    },
    Idempotent,
    Trace {
        label: Option<String>,
    },
    RuntimeTimeout(Duration),
    Heartbeat {
        interval: Duration,
        on_missing_count: u32,
    },
    Parallel,
    Ordered,
    MinResponses(u32),
    Custom {
        key: String,
        value: String,
    },
}

A typed annotation on a protocol statement.

Annotations provide metadata that affects code generation or runtime behavior without changing the core session type semantics.

Variants

TimedChoice

Timed choice: race an operation against a timeout.

When applied to a Choice, the choosing role races the operation against the specified duration. If timeout fires first, takes the TimedOut branch; otherwise takes the OnTime branch.

Fields

duration: Duration

Maximum time to wait before timing out.

Priority(u32)

Priority hint for scheduling.

Higher values indicate higher priority. Implementation-specific.

Retry

Retry count for transient failures.

Indicates how many times to retry the operation before failing.

Fields

max_attempts: u32

Maximum retry attempts.

delay: Option<Duration>

Optional delay between retries.

Idempotent

Mark a statement as idempotent (safe to retry).

Trace

Trace/debug annotation for logging.

Fields

label: Option<String>

Optional trace label for identification.

RuntimeTimeout(Duration)

Runtime timeout hint (for transport layer, not session type).

Unlike TimedChoice, this doesn’t affect the session type - it’s purely a hint to the transport layer.

Heartbeat

Heartbeat pattern: sender sends periodic heartbeats, receiver detects absence.

Desugars to a recursive choice where receiver decides liveness. The runtime uses interval for heartbeat timing and on_missing_count to determine when to declare the sender dead.

Fields

interval: Duration

Interval between heartbeats.

on_missing_count: u32

Number of missing heartbeats before declaring dead.

Parallel

Execute broadcast/collect operations in parallel.

When applied to a message with a wildcard/range destination, sends or receives are executed concurrently rather than sequentially.

Ordered

Preserve strict message ordering.

When applied to a collect operation, messages are returned in the order specified by the role list. This is the default behavior for sequential collect.

MinResponses(u32)

Minimum number of responses required for a collect operation.

When applied to a collect with wildcard/range source, the operation succeeds once at least min responses are received. Remaining responses are discarded or handled asynchronously.

Custom

Custom annotation for extensions or unknown types.

Falls back to key-value string pairs for extensibility.

Fields

key: String

The annotation key.

value: String

The annotation value.

Implementations

impl ProtocolAnnotation

pub fn timed_choice(duration: Duration) -> ProtocolAnnotation

Create a timed choice annotation from a duration.

pub fn timed_choice_ms(ms: u64) -> ProtocolAnnotation

Create a timed choice annotation from milliseconds.

pub fn priority(value: u32) -> ProtocolAnnotation

Create a priority annotation.

pub fn retry(max_attempts: u32) -> ProtocolAnnotation

Create a retry annotation with just max attempts.

pub fn retry_with_delay( max_attempts: u32, delay: Duration, ) -> ProtocolAnnotation

Create a retry annotation with delay between attempts.

pub fn trace() -> ProtocolAnnotation

Create a trace annotation without a label.

pub fn trace_labeled(label: impl Into<String>) -> ProtocolAnnotation

Create a trace annotation with a label.

pub fn runtime_timeout(duration: Duration) -> ProtocolAnnotation

Create a runtime timeout annotation.

pub fn heartbeat( interval: Duration, on_missing_count: u32, ) -> ProtocolAnnotation

Create a heartbeat annotation from a duration and missing count.

pub fn heartbeat_ms( interval_ms: u64, on_missing_count: u32, ) -> ProtocolAnnotation

Create a heartbeat annotation from milliseconds and missing count.

pub fn parallel() -> ProtocolAnnotation

Create a parallel annotation.

pub fn ordered() -> ProtocolAnnotation

Create an ordered annotation.

pub fn min_responses(min: u32) -> ProtocolAnnotation

Create a min_responses annotation.

pub fn custom( key: impl Into<String>, value: impl Into<String>, ) -> ProtocolAnnotation

Create a custom annotation.

pub fn is_timed_choice(&self) -> bool

Check if this is a timed choice annotation.

pub fn timed_choice_duration(&self) -> Option<Duration>

Get the timed choice duration, if this is a timed choice.

pub fn is_priority(&self) -> bool

Check if this is a priority annotation.

pub fn priority_value(&self) -> Option<u32>

Get the priority value, if this is a priority annotation.

pub fn is_retry(&self) -> bool

Check if this is a retry annotation.

pub fn retry_config(&self) -> Option<(u32, Option<Duration>)>

Get retry parameters, if this is a retry annotation.

pub fn is_idempotent(&self) -> bool

Check if this is an idempotent annotation.

pub fn is_trace(&self) -> bool

Check if this is a trace annotation.

pub fn is_heartbeat(&self) -> bool

Check if this is a heartbeat annotation.

pub fn heartbeat_params(&self) -> Option<(Duration, u32)>

Get the heartbeat parameters, if this is a heartbeat annotation.

pub fn is_runtime_timeout(&self) -> bool

Check if this is a runtime timeout annotation.

pub fn runtime_timeout_duration(&self) -> Option<Duration>

Get the runtime timeout duration, if this is a runtime timeout annotation.

pub fn is_parallel(&self) -> bool

Check if this is a parallel annotation.

pub fn is_ordered(&self) -> bool

Check if this is an ordered annotation.

pub fn is_min_responses(&self) -> bool

Check if this is a min_responses annotation.

pub fn min_responses_value(&self) -> Option<u32>

Get the min_responses value, if this is a min_responses annotation.

pub fn is_custom_key(&self, expected_key: &str) -> bool

Check if this is a custom annotation with the given key.

pub fn custom_value(&self, expected_key: &str) -> Option<&str>

Get the custom value if this is a custom annotation with the given key.

Trait Implementations

impl Clone for ProtocolAnnotation

fn clone(&self) -> ProtocolAnnotation

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for ProtocolAnnotation

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

Formats the value using the given formatter.

impl FromIterator<ProtocolAnnotation> for Annotations

fn from_iter<I>(iter: I) -> Annotations

where I: IntoIterator<Item = ProtocolAnnotation>,

Creates a value from an iterator.

impl PartialEq for ProtocolAnnotation

fn eq(&self, other: &ProtocolAnnotation) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl StructuralPartialEq for ProtocolAnnotation