Struct wasmtime_runtime::VMGcHeader

pub struct VMGcHeader(/* private fields */);

The common header for all objects allocated in a GC heap.

This header is shared across all collectors, although particular collectors may always add their own trailing fields to this header for all of their own GC objects.

This is a bit-packed structure that logically has the following fields:

struct VMGcHeader {
    // Highest 2 bits.
    kind: VMGcKind,

    // 30 bits available for the `GcRuntime` to make use of however it sees fit.
    reserved: u30,

    // The `VMSharedTypeIndex` for this GC object, if it isn't an
    // `externref` (or an `externref` re-wrapped as an `anyref`). `None` is
    // represented with `VMSharedTypeIndex::default()`.
    ty: Option<VMSharedTypeIndex>,
}

Implementations

impl VMGcHeader

pub fn externref() -> Self

Create the header for an externref.

pub fn kind(&self) -> VMGcKind

Get the kind of GC object that this is.

pub fn reserved_u30(&self) -> u32

Get the reserved 30 bits in this header.

These are bits are reserved for GcRuntime implementations to make use of however they see fit.

pub fn set_reserved_u30(&mut self, value: u32)

Set the 30-bit reserved value.

Panics

Panics if the given value has any of the upper 2 bits set.

pub unsafe fn unchecked_set_reserved_u30(&mut self, value: u32)

Set the 30-bit reserved value.

Safety

The given value must only use the lower 30 bits; its upper 2 bits must be unset.

pub fn ty(&self) -> Option<VMSharedTypeIndex>

Get this object’s specific concrete type.

Trait Implementations

impl GcHeapObject for VMGcHeader

fn is(_: &VMGcHeader) -> bool

Check whether the GC object with the given header is an instance of Self.