Struct Decision 

pub struct Decision {
    pub component: Arc<str>,
    pub mode: Mode,
    pub why: Why,
    pub carries: Ty,
    pub optimistic: bool,
    pub no_optimism: Option<NoOptimism>,
    pub per_session: bool,
    pub reads_presence: bool,
    pub span: Span,
}

How one component renders, and what follows from it.

Fields

component: Arc<str>

mode: Mode

why: Why

carries: Ty

What crosses to the browser: Html in Mode A, the fold’s accumulator in Mode B.

optimistic: bool

Whether the client may apply a command speculatively before the server answers.

no_optimism: Option<NoOptimism>

per_session: bool

True when the view reads the session — the fact that decides eligibility.

reads_presence: bool

True when the view reads presence(), which is the second fact that decides it.

span: Span

Where the component is declared, for a diagnostic.

Implementations

impl Decision

pub fn of( roles: &Roles, is_application: bool, declared: Option<(Mode, Span)>, span: Span, ) -> Decision

The decision for one component: what it declared, and what follows.

Takes the roles rather than the crate::split::Placed they end up in because this is what decides a field of that struct — and takes the declaration as an argument so that beck explain render, beck build and the checker cannot disagree about where it came from.

pub fn explain(&self, bundle: &Bundle) -> String

What beck explain render prints: the decision, what it puts on the wire, and what would change it.

The counterfactual is the useful half. A reader who wants Mode B and has Mode A needs to know whether one annotation would do it or whether the program’s shape refuses — and that is a question only the compiler can answer, because the answer is view_is_per_session.

pub fn refuse(&self, diags: &mut Diagnostics)

Refuse a component that may not render where it says it does.

One condition, and the reason there is only one is worth writing down. Mode B puts the accumulator on the wire, so the obvious second check is §3.5’s Sendable — and it is already discharged: a durable fold’s state must be storable (B0411), storable is strictly stronger than sendable (crate::secure), and the accumulator is what crosses. A secret[T] therefore cannot reach a Mode B client because it cannot reach the log, and a check here would be a second gate on a door that is shut. mode_b.rs asserts that composition rather than trusting it.

Trait Implementations

impl Clone for Decision

fn clone(&self) -> Decision

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Decision

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

Formats the value using the given formatter.