Struct UpVal 

pub struct UpVal {
    pub state: RefCell<UpValState>,
    /* 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.

Canonical state lives in two Cell fields (the tag and the open payload) plus a Cell<LuaValue> holding the closed payload. The state RefCell<UpValState> mirror is kept for cold consumers that still call slot() to inspect the open/closed shape. Scalar-to-scalar closed writes may leave the mirror’s scalar payload stale; callers that need the current closed value must use closed_value / try_closed_value. The split lets state.rs::upvalue_get / upvalue_set short-circuit the Open path with zero RefCell borrow overhead, which is the dominant cost in fibonacci-class recursion benchmarks.

Fields

state: RefCell<UpValState>

Implementations

impl UpVal

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

pub fn closed(v: LuaValue) -> UpVal

pub fn slot(&self) -> Ref<'_, UpValState>

Backwards-compat handle on the full UpValState. Out-of-crate code matches against this through Ref::deref. Hot-path callers should use try_open_payload / closed_value instead.

pub fn is_open(&self) -> bool

pub fn is_closed(&self) -> bool

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

Zero-RefCell fast path used by upvalue_get / upvalue_set. Returns Some((thread_id, idx)) when the upvalue is still open, None otherwise.

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<(), Error>

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)