Enum rustc_target::abi::TagEncoding

pub enum TagEncoding {
    Direct,
    Niche {
        dataful_variant: VariantIdx,
        niche_variants: RangeInclusive<VariantIdx>,
        niche_start: u128,
    },
}

Variants

Direct

The tag directly stores the discriminant, but possibly with a smaller layout (so converting the tag to the discriminant can require sign extension).

Niche

Niche (values invalid for a type) encoding the discriminant: Discriminant and variant index coincide. The variant dataful_variant contains a niche at an arbitrary offset (field tag_field of the enum), which for a variant with discriminant d is set to (d - niche_variants.start).wrapping_add(niche_start).

For example, Option<(usize, &T)> is represented such that None has a null pointer for the second tuple field, and Some is the identity function (with a non-null reference).

Fields of Niche

dataful_variant: VariantIdxniche_variants: RangeInclusive<VariantIdx>niche_start: u128

Trait Implementations

impl Debug for TagEncoding

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

Formats the value using the given formatter.

impl Hash for TagEncoding

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given Hasher.

impl<__CTX> HashStable<__CTX> for TagEncoding where
    __CTX: HashStableContext, 

fn hash_stable(&self, __hcx: &mut __CTX, __hasher: &mut StableHasher)

impl PartialEq<TagEncoding> for TagEncoding

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

This method tests for self and other values to be equal, and is used by ==.

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

This method tests for !=.

impl Eq for TagEncoding

impl StructuralEq for TagEncoding

impl StructuralPartialEq for TagEncoding