Enum ProjectionError 

pub enum ProjectionError {
    SelfMessage {
        role: Role,
    },
    EmptyChoice {
        from: Role,
        to: Role,
    },
    MergeFailed {
        role: Role,
        labels: (String, String),
        left: Box<SessionType>,
        right: Box<SessionType>,
    },
    UnboundVariable(String),
}

Negative verdict of the projection / safe-realizability gate.

Variants

SelfMessage

from == to for some message or choice — protocols at the global layer don’t model self-talk (it would have no observable effect; the §41.a algebra has no operational rule for it).

Fields

role: Role

EmptyChoice

Choice { arms: {} } — a choice with no arms has no projection for the chooser (no internal-choice arm to select).

Fields

from: Role

to: Role

MergeFailed

The merge condition failed: a role r that doesn’t participate in a choice p → q saw arms that project to non-equivalent local types, so it cannot observe which branch p chose. The protocol is unrealizable.

Fields

role: Role

The role whose projection diverged across arms.

labels: (String, String)

The two labels whose continuations disagree (deterministic pick: alphabetically first divergent pair).

left: Box<SessionType>

The two projections that fail to merge — useful for the type-checker’s diagnostic.

right: Box<SessionType>

UnboundVariable(String)

Var(x) reached outside any enclosing Rec(x, _). The global type is open and has no closed-form projection.

Trait Implementations

impl Clone for ProjectionError

fn clone(&self) -> ProjectionError

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for ProjectionError

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

Formats the value using the given formatter.

impl Display for ProjectionError

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

Formats the value using the given formatter.

impl Eq for ProjectionError

impl Error for ProjectionError

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn description(&self) -> &str

👎Deprecated since 1.42.0:

use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)

Provides type-based access to context intended for error reports.

impl PartialEq for ProjectionError

fn eq(&self, other: &ProjectionError) -> 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 ProjectionError