Struct LuaUserDataImpl 

pub struct LuaUserDataImpl {
    pub len: usize,
    pub nuvalue: u16,
    pub metatable: Option<()>,
    pub uv: Vec<()>,
    pub data: Box<[u8]>,
}

Full userdata: a GC-tracked object carrying a raw byte payload plus optional Lua user values and an optional metatable.

C mapping (types.tsv)

Udata           → LuaUserData
Udata.len       → len: usize
Udata.nuvalue   → nuvalue: u16  (covered by uv.len() but kept for parity)
Udata.metatable → metatable: Option<GcRef<LuaTable>>
Udata.uv        → uv: Vec<LuaValue>
(no direct C field) data: Box<[u8]>  — the raw byte payload; C used a flexible
                         array member laid out past the Udata header via
                         `udatamemoffset` alignment math.

Fields

len: usize

nuvalue: u16

metatable: Option<()>

uv: Vec<()>

data: Box<[u8]>

Trait Implementations

impl Trace for LuaUserDataImpl

Phase-B internal userdata. Both metatable and uv are currently Option<()> / Vec<()> stubs — no GC edges to walk yet. Becomes real when userdata machinery lands post-D-1.

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)