Enum rustc_abi::TagEncoding

pub enum TagEncoding<V: Idx> {
    Direct,
    Niche {
        untagged_variant: V,
        niche_variants: RangeInclusive<V>,
        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

Fields

untagged_variant: V

niche_variants: RangeInclusive<V>

niche_start: u128

Niche (values invalid for a type) encoding the discriminant: Discriminant and variant index coincide. The variant untagged_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).

Trait Implementations

impl<V: Clone + Idx> Clone for TagEncoding<V>

fn clone(&self) -> TagEncoding<V>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<V: Debug + Idx> Debug for TagEncoding<V>

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

Formats the value using the given formatter.

impl<V: Hash + Idx> Hash for TagEncoding<V>

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,
    Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<V, __CTX> HashStable<__CTX> for TagEncoding<V>where
    __CTX: HashStableContext,
    V: HashStable<__CTX> + Idx,

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

impl<V: PartialEq + Idx> PartialEq<TagEncoding<V>> for TagEncoding<V>

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

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

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

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

impl<V: Eq + Idx> Eq for TagEncoding<V>

impl<V: Idx> StructuralEq for TagEncoding<V>

impl<V: Idx> StructuralPartialEq for TagEncoding<V>

Layout

Note: Unable to compute type layout, possibly due to this type having generic parameters. Layout can only be computed for concrete, fully-instantiated types.