# Enum rustc_target::abi::FieldsShape

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    pub enum FieldsShape<FieldIdx>where
        FieldIdx: Idx,{
        Primitive,
        Union(NonZeroUsize),
        Array {
            stride: Size,
            count: u64,
        },
        Arbitrary {
            offsets: IndexVec<FieldIdx, Size>,
            memory_index: IndexVec<FieldIdx, u32>,
        },
    }

Expand description

Describes how the fields of a type are located in memory.

## Variants§

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### Primitive

Scalar primitives and `!`, which never have fields.

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### Union(NonZeroUsize)

All fields start at no offset. The `usize` is the field count.

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### Array

#### Fields

§`stride: Size`
§`count: u64`

Array/vector-like placement, with all fields of identical types.

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### Arbitrary

#### Fields

§`offsets: IndexVec<FieldIdx, Size>`

Offsets for the first byte of each field, ordered to match the source definition order. This vector does not go in increasing order.

§`memory_index: IndexVec<FieldIdx, u32>`

Maps source order field indices to memory order indices, depending on how the fields were reordered (if at all). This is a permutation, with both the source order and the memory order using the same (0..n) index ranges.

Note that during computation of `memory_index`, sometimes it is easier to operate on the inverse mapping (that is, from memory order to source order), and that is usually named `inverse_memory_index`.

Struct-like placement, with precomputed offsets.

Fields are guaranteed to not overlap, but note that gaps before, between and after all the fields are NOT always padding, and as such their contents may not be discarded. For example, enum variants leave a gap at the start, where the discriminant field in the enum layout goes.

## Auto Trait Implementations§

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### impl<FieldIdx> RefUnwindSafe for FieldsShape<FieldIdx>

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### impl<FieldIdx> Send for FieldsShape<FieldIdx>

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### impl<FieldIdx> Sync for FieldsShape<FieldIdx>

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### impl<FieldIdx> Unpin for FieldsShape<FieldIdx>

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### impl<FieldIdx> UnwindSafe for FieldsShape<FieldIdx>

## Blanket Implementations§

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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<T> From<T> for T

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

Returns the argument unchanged.

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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> 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.

## 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: 48 bytes

Size for each variant:

- `Primitive`: 0 bytes
- `Union`: 8 bytes
- `Array`: 16 bytes
- `Arbitrary`: 48 bytes