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

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference’s “Type Layout” chapter for details on type layout guarantees.

Size: 32 bytes

Size for each variant:

• Direct: 0 bytes
• Niche: 32 bytes