pub const INLINE_UPVALS_N: usize = 2;Expand description
P11-S5d.M — closures with ≤ INLINE_UPVALS_N upvalues skip the
per-closure upvals Box. The Op::Closure handler builds upvals
into a stack array and calls Heap::new_closure_inline(&[Gc<…>]),
which writes them straight into inline_storage — no caller-side
Vec/Box. closure_alloc-style benchmarks create 10k single-upval
closures per iter; eliminating the 24-byte Vec alloc shaves ~300µs.