LayoutData in rustc_abi - Rust
Description: API documentation for the Rust `LayoutData` struct in crate `rustc_abi`.

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## LayoutData

# Struct LayoutData

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    pub struct LayoutData<FieldIdx: Idx, VariantIdx: Idx> {
        pub fields: FieldsShape<FieldIdx>,
        pub variants: Variants<FieldIdx, VariantIdx>,
        pub backend_repr: BackendRepr,
        pub largest_niche: Option<Niche>,
        pub uninhabited: bool,
        pub align: AbiAlign,
        pub size: Size,
        pub max_repr_align: Option<Align>,
        pub unadjusted_abi_align: Align,
        pub randomization_seed: Hash64,
    }

## Fields§

§`fields: FieldsShape<FieldIdx>`

Says where the fields are located within the layout.

§`variants: Variants<FieldIdx, VariantIdx>`

Encodes information about multi-variant layouts. Even with `Multiple` variants, a layout still has its own fields! Those are then shared between all variants. One of them will be the discriminant, but e.g. coroutines can have more.

To access all fields of this layout, both `fields` and the fields of the active variant must be taken into account.

§`backend_repr: BackendRepr`

The `backend_repr` defines how this data will be represented to the codegen backend, and encodes value restrictions via `valid_range`.

Note that this is entirely orthogonal to the recursive structure defined by `variants` and `fields`; for example, `ManuallyDrop<Result<isize, isize>>` has `IrForm::ScalarPair`! So, even with non-`Memory` `backend_repr`, `fields` and `variants` have to be taken into account to find all fields of this layout.

§`largest_niche: Option<Niche>`

The leaf scalar with the largest number of invalid values (i.e. outside of its `valid_range`), if it exists.

§`uninhabited: bool`

Is this type known to be uninhabted?

This is separate from BackendRepr because uninhabited return types can affect ABI, especially in the case of by-pointer struct returns, which allocate stack even when unused.

§`align: AbiAlign`§`size: Size`§`max_repr_align: Option<Align>`

The largest alignment explicitly requested with `repr(align)` on this type or any field. Only used on i686-windows, where the argument passing ABI is different when alignment is requested, even if the requested alignment is equal to the natural alignment.

§`unadjusted_abi_align: Align`

The alignment the type would have, ignoring any `repr(align)` but including `repr(packed)`. Only used on aarch64-linux, where the argument passing ABI ignores the requested alignment in some cases.

§`randomization_seed: Hash64`

The randomization seed based on this type’s own repr and its fields.

Since randomization is toggled on a per-crate basis even crates that do not have randomization enabled should still calculate a seed so that downstream uses can use it to distinguish different types.

For every T and U for which we do not guarantee that a repr(Rust) `Foo<T>` can be coerced or transmuted to `Foo<U>` we aim to create probalistically distinct seeds so that Foo can choose to reorder its fields based on that information. The current implementation is a conservative approximation of this goal.

## Implementations§

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### impl<FieldIdx: Idx, VariantIdx: Idx> LayoutData<FieldIdx, VariantIdx>

“Simple” layout constructors that cannot fail.

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#### pub fn unit<C: HasDataLayout>(cx: &C, sized: bool) -> Self

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#### pub fn never_type<C: HasDataLayout>(cx: &C) -> Self

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#### pub fn scalar<C: HasDataLayout>(cx: &C, scalar: Scalar) -> Self

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#### pub fn scalar_pair<C: HasDataLayout>(cx: &C, a: Scalar, b: Scalar) -> Self

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#### pub fn uninhabited_variant<C: HasDataLayout>( cx: &C, index: VariantIdx, fields: usize, ) -> Self

Returns a dummy layout for an uninhabited variant.

Uninhabited variants get pruned as part of the layout calculation, so this can be used after the fact to reconstitute a layout.

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#### pub fn for_variant(parent: &Self, index: VariantIdx) -> Self

Returns a layout for an inhabited variant.

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### impl<FieldIdx: Idx, VariantIdx: Idx> LayoutData<FieldIdx, VariantIdx>

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#### pub fn is_aggregate(&self) -> bool

Returns `true` if this is an aggregate type (including a ScalarPair!)

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#### pub fn is_uninhabited(&self) -> bool

Returns `true` if this is an uninhabited type

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### impl<FieldIdx: Idx, VariantIdx: Idx> LayoutData<FieldIdx, VariantIdx>

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#### pub fn is_unsized(&self) -> bool

Returns `true` if the layout corresponds to an unsized type.

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#### pub fn is_sized(&self) -> bool

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#### pub fn is_1zst(&self) -> bool

Returns `true` if the type is sized and a 1-ZST (meaning it has size 0 and alignment 1).

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#### pub fn is_scalable_vector(&self) -> bool

Returns `true` if the size of the type is only known at runtime.

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#### pub fn scalable_vector_element_count(&self) -> Option<u64>

Returns the elements count of a scalable vector.

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#### pub fn is_zst(&self) -> bool

Returns `true` if the type is a ZST and not unsized.

Note that this does not imply that the type is irrelevant for layout! It can still have non-trivial alignment constraints. You probably want to use `is_1zst` instead.

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#### pub fn eq_abi(&self, other: &Self) -> bool

Checks if these two `Layout` are equal enough to be considered “the same for all function call ABIs”. Note however that real ABIs depend on more details that are not reflected in the `Layout`; the `PassMode` need to be compared as well. Also note that we assume aggregates are passed via `PassMode::Indirect` or `PassMode::Cast`; more strict checks would otherwise be required.

## Trait Implementations§

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### impl<'a, Ty> AsRef<LayoutData<FieldIdx, VariantIdx>> for TyAndLayout<'a, Ty>

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#### fn as_ref(&self) -> &LayoutData<FieldIdx, VariantIdx>

Converts this type into a shared reference of the (usually inferred) input type.
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### impl<FieldIdx: Clone + Idx, VariantIdx: Clone + Idx> Clone for LayoutData<FieldIdx, VariantIdx>

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#### fn clone(&self) -> LayoutData<FieldIdx, VariantIdx>

Returns a duplicate of the value. Read more
1.0.0 (const: unstable) · Source§

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

Performs copy-assignment from `source`. Read more
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### impl<FieldIdx: Idx, VariantIdx: Idx> Debug for LayoutData<FieldIdx, VariantIdx>
where FieldsShape<FieldIdx>: Debug, Variants<FieldIdx, VariantIdx>: Debug,

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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<FieldIdx: Eq + Idx, VariantIdx: Eq + Idx> Eq for LayoutData<FieldIdx, VariantIdx>

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### impl<FieldIdx: Hash + Idx, VariantIdx: Hash + Idx> Hash for LayoutData<FieldIdx, VariantIdx>

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

Feeds this value into the given `Hasher`. Read more
1.3.0 · Source§

#### 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<FieldIdx: PartialEq + Idx, VariantIdx: PartialEq + Idx> PartialEq for LayoutData<FieldIdx, VariantIdx>

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

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 (const: unstable) · Source§

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

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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### impl<FieldIdx, VariantIdx> StableHash for LayoutData<FieldIdx, VariantIdx>
where FieldIdx: StableHash + Idx, VariantIdx: StableHash + Idx,

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#### fn stable_hash<__Hcx: StableHashCtxt>( &self, __hcx: &mut __Hcx, __hasher: &mut StableHasher, )

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### impl<FieldIdx: Idx, VariantIdx: Idx> StructuralPartialEq for LayoutData<FieldIdx, VariantIdx>

## Auto Trait Implementations§

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### impl<FieldIdx, VariantIdx> DynSend for LayoutData<FieldIdx, VariantIdx>
where VariantIdx: DynSend, FieldIdx: DynSend,

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### impl<FieldIdx, VariantIdx> DynSync for LayoutData<FieldIdx, VariantIdx>
where VariantIdx: DynSync, FieldIdx: DynSync,

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### impl<FieldIdx, VariantIdx> Freeze for LayoutData<FieldIdx, VariantIdx>
where VariantIdx: Freeze, FieldIdx: Freeze,

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### impl<FieldIdx, VariantIdx> RefUnwindSafe for LayoutData<FieldIdx, VariantIdx>
where VariantIdx: RefUnwindSafe, FieldIdx: RefUnwindSafe,

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### impl<FieldIdx, VariantIdx> Send for LayoutData<FieldIdx, VariantIdx>
where VariantIdx: Send, FieldIdx: Send,

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### impl<FieldIdx, VariantIdx> Sync for LayoutData<FieldIdx, VariantIdx>
where VariantIdx: Sync, FieldIdx: Sync,

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### impl<FieldIdx, VariantIdx> Unpin for LayoutData<FieldIdx, VariantIdx>
where VariantIdx: Unpin, FieldIdx: Unpin,

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### impl<FieldIdx, VariantIdx> UnsafeUnpin for LayoutData<FieldIdx, VariantIdx>
where VariantIdx: UnsafeUnpin, FieldIdx: UnsafeUnpin,

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### impl<FieldIdx, VariantIdx> UnwindSafe for LayoutData<FieldIdx, VariantIdx>
where VariantIdx: UnwindSafe, FieldIdx: 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> AnyEq for T
where T: Any + PartialEq,

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#### fn equals(&self, other: &(dyn Any + 'static)) -> bool

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#### fn as_any(&self) -> &(dyn Any + 'static)

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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<T> CloneToUninit for T
where T: Clone,

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#### unsafe fn clone_to_uninit(&self, dest: *mut u8)

🔬This is a nightly-only experimental API. (`clone_to_uninit`)
Performs copy-assignment from `self` to `dest`. 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> ErasedDestructor for T
where T: 'static,

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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> IntoEither for T

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#### fn into_either(self, into_left: bool) -> Either<Self, Self>

Converts `self` into a `Left` variant of `Either<Self, Self>` if `into_left` is `true`. Converts `self` into a `Right` variant of `Either<Self, Self>` otherwise. Read more
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#### fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
where F: FnOnce(&Self) -> bool,

Converts `self` into a `Left` variant of `Either<Self, Self>` if `into_left(&self)` returns `true`. Converts `self` into a `Right` variant of `Either<Self, Self>` otherwise. Read more
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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> Same for T

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#### type Output = T

Should always be `Self`
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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

## 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.