Struct NativeClosure 

pub struct NativeClosure {
    pub f: NativeFn,
    pub upvals: Box<[Value]>,
    pub is_async: bool,
    /* private fields */
}

A native (host) function with captured upvalues — the analogue of PUC C closures. Builtins are allocated once at registration so identity is stable; stateful iterators (gmatch) mutate their upvalues via as_mut.

Fields

f: NativeFn

The host function pointer this closure dispatches to.

upvals: Box<[Value]>

Captured upvalues, visible inside f via the Vm’s call API.

is_async: bool

v1.1 B10 Stage 2 — marker bit for async natives. When true, f is actually an crate::vm::async_drive::AsyncNativeFn (same pointer width, transmuted at the call site) returning a Pin<Box<dyn Future>>. The dispatcher’s native-call path checks this bit and routes through the cooperative-yield mechanism instead of invoking f synchronously. Default false (sync native) for all v1.0 / v1.1-Stage-1 construction sites.