Enum VMGcKind

#[repr(u32)]
pub enum VMGcKind {
    ExternRef = 1_073_741_824,
    AnyRef = 2_147_483_648,
    EqRef = 2_684_354_560,
    ArrayRef = 2_818_572_288,
    StructRef = 2_952_790_016,
}

The kind of an object in a GC heap.

Note that this type is accessed from Wasm JIT code.

VMGcKind is a bitset where to test if a is a subtype of an “abstract-ish” type b, we can simply use a single bitwise-and operation:

a <: b   iff   a & b == b

For example, because VMGcKind::AnyRef has the high bit set, every kind representing some subtype of anyref also has its high bit set.

We say “abstract-ish” type because in addition to the abstract heap types (other than i31) we also have variants for externrefs that have been converted into an anyref via extern.convert_any and externrefs that have been converted into an anyref via any.convert_extern. Note that in the latter case, because any.convert_extern $foo produces a value that is not an instance of eqref, VMGcKind::AnyOfExternRef & VMGcKind::EqRef != VMGcKind::EqRef.

Furthermore, this type only uses the highest 6 bits of its u32 representation, allowing the lower 27 bytes to be bitpacked with other stuff as users see fit.

Variants

ExternRef = 1_073_741_824

AnyRef = 2_147_483_648

EqRef = 2_684_354_560

ArrayRef = 2_818_572_288

StructRef = 2_952_790_016

Implementations

impl VMGcKind

pub const MASK: u32 = 4_160_749_568u32

Mask this value with a u32 to get just the bits that VMGcKind uses.

pub const UNUSED_MASK: u32 = 134_217_727u32

Mask this value with a u32 that potentially contains a VMGcKind to get the bits that VMGcKind doesn’t use.

pub fn value_fits_in_unused_bits(value: u32) -> bool

Does the given value fit in the unused bits of a VMGcKind?

pub fn from_high_bits_of_u32(val: u32) -> VMGcKind

Convert the given value into a VMGcKind by masking off the unused bottom bits.

pub fn matches(self, other: Self) -> bool

Does this kind match the other kind?

That is, is this kind a subtype of the other kind?

pub fn as_u32(self) -> u32

Get this VMGcKind as a raw u32.

Trait Implementations

impl Clone for VMGcKind

fn clone(&self) -> VMGcKind

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for VMGcKind

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for VMGcKind

fn eq(&self, other: &VMGcKind) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for VMGcKind

impl Eq for VMGcKind

impl StructuralPartialEq for VMGcKind