Struct VecPayload 

#[repr(C)]
pub struct VecPayload {
    pub element_descriptor: *const TypeDescriptor,
    pub items: ReprCVec<GcRef>,
}

The Vec[T] payload: the element descriptor plus the growable items.

items grows in place (§11.1) and is Drop, so VEC’s drop_value releases its buffer on sweep (§12.5). The element descriptor is a 'static borrow and owns nothing.

Fields

element_descriptor: *const TypeDescriptor

The descriptor for every element in items, or null when this vector has not been told its element type. Read by trace/format/equals to dispatch without a scattered type switch (§11.4); read it through VecPayload::element, not directly.

Null is the honest encoding of “unknown”, and it only survives while the vector is empty: the first push adopts the pushed value’s descriptor. A vector that has been told its element type is never retagged.

items: ReprCVec<GcRef>

The elements, in order. Growable (not Box<[T]>) so push mutates in place, and a ReprCVec rather than a std::Vec so the length and the element pointer are at offsets generated code is allowed to know (ADR-118). std::Vec is #[repr(Rust)] and hides both inside a private RawVec.

Implementations

impl VecPayload

pub fn element(&self) -> Option<&'static TypeDescriptor>

The element descriptor, or None if this vector was never told its element type. None implies items is empty.

[ElementSeq::element] is the body; this forwarder is the public spelling, and it exists because [ElementSeq] is pub(crate) while one caller is not: praxis-codegen-cranelift’s adversarial audit reads an empty Vec[Float]’s descriptor through this method, which is the check that codegen labelled the vector before any push could repair it.