Struct UpVal 

pub struct UpVal { /* private fields */ }

A closure upvalue. Open upvalues point at a slot on a thread’s stack (referred to by index, since the stack reallocates). Closed upvalues own the value.

State lives entirely in three Cell fields and is single-source-of-truth. open_thread_id doubles as the open/closed discriminant: a non-negative value is the owning thread id of an open upvalue; the [CLOSED_TAG] sentinel (-1) means the upvalue is closed and its payload is in closed_value. Valid thread ids are non-negative (the main thread is id 0), so the sentinel is unambiguous. open_idx is the stack slot of an open upvalue. Closing is terminal — there is no re-open path — so a CLOSED_TAG tag never reverts.

Read the open shape with try_open_payload (None once closed) and the closed payload with closed_value / try_closed_value. The all-Cell layout lets state.rs::upvalue_get / upvalue_set short-circuit the Open path with zero borrow-guard overhead, which is the dominant cost in fibonacci-class recursion benchmarks.

Implementations

impl UpVal

pub fn open(thread_id: usize, idx: StackIdx) -> Self

pub fn closed(v: LuaValue) -> Self

pub fn is_open(&self) -> bool

pub fn is_closed(&self) -> bool

pub fn try_open_payload(&self) -> Option<(usize, StackIdx)>

Zero-overhead read of the open shape used by upvalue_get / upvalue_set and every out-of-crate consumer that inspects an open upvalue’s (thread_id, idx). Returns Some((thread_id, idx)) when the upvalue is still open, None once it has been closed.

pub fn closed_value(&self) -> LuaValue

Returns the closed-side value. Callers must have confirmed the upvalue is closed (try_open_payload returned None).

pub fn close_with(&self, v: LuaValue)

pub fn set_closed_value(&self, v: LuaValue)

pub fn try_closed_value(&self) -> Option<LuaValue>

Trait Implementations

impl Debug for UpVal

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

Formats the value using the given formatter.

impl Trace for UpVal

UpVal — Open (refers to a thread stack slot by index) or Closed (owns a LuaValue). The Open variant carries no direct GC reference; the slot it points at is traced through the owning thread’s stack walk.

fn type_name(&self) -> &'static str

Concrete Rust type name for diagnostic/testC telemetry (Heap::type_name_count). Collector behavior must not branch on this. The default covers container blanket impls, which are never GC-boxed directly; concrete runtime types override it with std::any::type_name::<Self>().

fn trace(&self, m: &mut Marker)