# Enum rustc_abi::TagEncoding

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

## Variants§

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### Direct

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

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### Niche

#### Fields

§`untagged_variant: VariantIdx`
§`niche_variants: RangeInclusive<VariantIdx>`
§`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§

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### impl<VariantIdx: Clone + Idx> Clone for TagEncoding<VariantIdx>

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#### fn clone(&self) -> TagEncoding<VariantIdx>

Returns a copy of the value. Read more
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#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
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### impl<VariantIdx: Debug + Idx> Debug for TagEncoding<VariantIdx>

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

Formats the value using the given formatter. Read more
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### impl<VariantIdx: Hash + Idx> Hash for TagEncoding<VariantIdx>

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

Feeds this value into the given `Hasher`. Read more
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#### fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given `Hasher`. Read more
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### impl<VariantIdx, __CTX> HashStable<__CTX> for TagEncoding<VariantIdx>
where __CTX: HashStableContext, VariantIdx: HashStable<__CTX> + Idx,

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

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### impl<VariantIdx: PartialEq + Idx> PartialEq for TagEncoding<VariantIdx>

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

This method tests for `self` and `other` values to be equal, and is used by `==`.
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#### 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.
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### impl<VariantIdx: Eq + Idx> Eq for TagEncoding<VariantIdx>

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### impl<VariantIdx: Idx> StructuralPartialEq for TagEncoding<VariantIdx>

## Auto Trait Implementations§

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### impl<VariantIdx> DynSend for TagEncoding<VariantIdx>
where VariantIdx: DynSend,

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### impl<VariantIdx> DynSync for TagEncoding<VariantIdx>
where VariantIdx: DynSync,

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### impl<VariantIdx> Freeze for TagEncoding<VariantIdx>
where VariantIdx: Freeze,

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### impl<VariantIdx> RefUnwindSafe for TagEncoding<VariantIdx>
where VariantIdx: RefUnwindSafe,

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### impl<VariantIdx> Send for TagEncoding<VariantIdx>
where VariantIdx: Send,

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### impl<VariantIdx> Sync for TagEncoding<VariantIdx>
where VariantIdx: Sync,

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### impl<VariantIdx> Unpin for TagEncoding<VariantIdx>
where VariantIdx: Unpin,

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### impl<VariantIdx> UnwindSafe for TagEncoding<VariantIdx>
where VariantIdx: UnwindSafe,

## Blanket Implementations§

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### impl<T> Aligned for T

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#### const ALIGN: Alignment = _

Alignment of `Self`.
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### impl<T> Any for T
where T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for T
where T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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#### fn equivalent(&self, key: &K) -> bool

Checks if this value is equivalent to the given key. Read more
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### impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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#### fn equivalent(&self, key: &K) -> bool

Checks if this value is equivalent to the given key. Read more
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### impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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#### fn equivalent(&self, key: &K) -> bool

Compare self to `key` and return `true` if they are equal.
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T> Instrument for T

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#### fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided `Span`, returning an `Instrumented` wrapper. Read more
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#### fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current `Span`, returning an `Instrumented` wrapper. Read more
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### impl<T, U> Into<U> for T
where U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T> Pointable for T

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#### const ALIGN: usize = _

The alignment of pointer.
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#### type Init = T

The type for initializers.
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#### unsafe fn init(init: <T as Pointable>::Init) -> usize

Initializes a with the given initializer. Read more
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#### unsafe fn deref<'a>(ptr: usize) -> &'a T

Dereferences the given pointer. Read more
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#### unsafe fn deref_mut<'a>(ptr: usize) -> &'a mut T

Mutably dereferences the given pointer. Read more
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#### unsafe fn drop(ptr: usize)

Drops the object pointed to by the given pointer. Read more
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### impl<T> ToOwned for T
where T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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### impl<T, U> TryFrom<U> for T
where U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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### impl<V, T> VZip<V> for T
where V: MultiLane<T>,

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#### fn vzip(self) -> V

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### impl<T> WithSubscriber for T

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#### fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
where S: Into<Dispatch>,

Attaches the provided `Subscriber` to this type, returning a `WithDispatch` wrapper. Read more
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#### fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default `Subscriber` to this type, returning a `WithDispatch` wrapper. Read more
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### impl<'a, T> Captures<'a> for T
where T: ?Sized,

## 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.