pub enum FieldsShape {
    Primitive,
    Union(NonZeroUsize),
    Array {
        stride: Size,
        count: u64,
    },
    Arbitrary {
        offsets: Vec<Size>,
        memory_index: Vec<u32>,
    },
}
Expand description

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

Variants§

§

Primitive

Scalar primitives and !, which never have fields.

§

Union(NonZeroUsize)

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

§

Array

Fields

§stride: Size
§count: u64

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

§

Arbitrary

Fields

§offsets: Vec<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: Vec<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.

Implementations§

Gets source indices of the fields by increasing offsets.

Trait Implementations§

Returns a copy of the value. Read more
Performs copy-assignment from source. Read more
Formats the value using the given formatter. Read more
Feeds this value into the given Hasher. Read more
Feeds a slice of this type into the given Hasher. Read more
This method tests for self and other values to be equal, and is used by ==.
This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

Auto Trait Implementations§

Blanket Implementations§

Gets the TypeId of self. Read more
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

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

The resulting type after obtaining ownership.
Creates owned data from borrowed data, usually by cloning. Read more
Uses borrowed data to replace owned data, usually by cloning. Read more
The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion 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: 56 bytes

Size for each variant:

  • Primitive: 0 bytes
  • Union: 8 bytes
  • Array: 16 bytes
  • Arbitrary: 48 bytes