Struct FnRow 

pub struct FnRow(/* private fields */);

The effect row riding a Ty::Fn — docs/effects-spec.md §5 (“rows ride the unifier — the heap answer”), issue #1680 step 3.

What a row is, concretely. §7 rules that “the runtime never computes a row … a live fn value is a token; its row is a table lookup” in the shipped DefinitionId → row table. So the thing a type has to carry is not a computed EffectRow but the set of in-project creation targets whose fn values may inhabit the slot — the keys that table is looked up by. §6.1a is what makes that the right (and the only acyclic) choice: “§6.1 fixes every fn value’s row at its creation site and creation sites are syntactic: #fn(g) names g literally, and bind copies from an already-known value rather than naming a new target.” A target set is therefore structural evidence, never an inferred row, so growing it onto Ty cannot put an inferred row inside the call_graph → scc_membership → solve_scc fixpoint the way Fork A’s rejected shape would have.

The lattice. unknown is the top element (the conservative-total floor of §3): “some fn value from a source this slot’s type cannot name may reach here”. FnRow::join is set union with unknown absorbing, which is exactly §5’s “a cell or collection’s element type accumulates the join of every fn value assigned into it, through copies, parameters, returns, and nesting”. That absorption is on the unknown row, not on every untraceable-looking write: a write typed plain Ty::Unknown (an unresolved reference, or an unregistered EXTERNAL’s return) unifies through Ty::Unknown’s own identity arm, not through this lattice at all, and so leaves the other operand’s row untouched rather than poisoning it to unknown.

Not yet read by the effect walk. def_effect_atoms deliberately runs the body walk with empty globals and empty signatures (§6.1a’s acyclicity is load-bearing on that), so a #fn literal types as Unknown there and this row is invisible to effect inference as currently constructed. Wiring §6 mechanism 3 — the heap — means deciding which stratum reads the type-carried row, which the 2026-07-28 sitting did not settle; see docs/effects-spec.md §6.1c.

Represented as an Option<Box<…>> so the common Ty::Fn stays one pointer wider rather than three words wider — Ty is copied constantly through the join.

Implementations

impl FnRow

pub fn unknown() -> Self

The top element: nothing is known about where the values inhabiting this slot were created. Also Default, so every Ty::Fn built without explicit creation evidence is conservative by construction.

pub fn of_target(target: DefinitionId) -> Self

The row of a fn value created here, at a #fn(target, …) literal naming target — the one syntactic creation form (§6.1a).

pub fn empty() -> Self

The empty row: this slot provably holds no in-project fn value. Only reachable through a join that started here; never minted directly.

pub fn is_unknown(&self) -> bool

true when this row is the top element (FnRow::unknown).

pub fn targets(&self) -> Option<&BTreeSet<DefinitionId>>

The creation targets, or None when the row is the top element. A caller that wants the conservative reading must treat None as “every target”, never as “no targets”.

pub fn join(&self, other: &FnRow) -> FnRow

Least upper bound: union of the target sets, with the top element absorbing. Monotone over a finite per-project lattice, so folding it through unify terminates for the same reason the rest of the join does.

Trait Implementations

impl Clone for FnRow

fn clone(&self) -> FnRow

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for FnRow

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

Formats the value using the given formatter.

impl Default for FnRow

fn default() -> FnRow

Returns the “default value” for a type.

impl Eq for FnRow

impl Hash for FnRow

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for FnRow

fn cmp(&self, other: &FnRow) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

fn clamp_to<R>(self, range: R) -> Self

where Self: Sized, R: ClampBounds<Self>,

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

Restrict a value to a certain range.

impl PartialEq for FnRow

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

Equality operator ==.

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

Inequality operator !=.

impl PartialOrd for FnRow

fn partial_cmp(&self, other: &FnRow) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

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

Tests less than (for self and other) and is used by the < operator.

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

Tests less than or equal to (for self and other) and is used by the <= operator.

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

Tests greater than (for self and other) and is used by the > operator.

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

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl StructuralPartialEq for FnRow