Trait rkyv::ArchiveUnsized [−][src]
pub trait ArchiveUnsized: Pointee { type Archived: ArchivePointee + ?Sized; type MetadataResolver; unsafe fn resolve_metadata(
&self,
pos: usize,
resolver: Self::MetadataResolver,
out: *mut ArchivedMetadata<Self>
); unsafe fn resolve_unsized(
&self,
from: usize,
to: usize,
resolver: Self::MetadataResolver,
out: *mut RelPtr<Self::Archived>
) { ... } }
Expand description
A counterpart of Archive
that’s suitable for unsized types.
Instead of archiving its value directly, ArchiveUnsized
archives a RelPtr
to its archived
type. As a consequence, its resolver must be usize
.
ArchiveUnsized
is automatically implemented for all types that implement Archive
.
ArchiveUnsized
is already implemented for slices and string slices, and the rkyv_dyn
crate
can be used to archive trait objects. Other unsized types must manually implement
ArchiveUnsized
.
Examples
use core::{mem::transmute, ops::{Deref, DerefMut}}; use ptr_meta::Pointee; use rkyv::{ from_archived, to_archived, archived_unsized_value, ser::{serializers::AlignedSerializer, Serializer}, AlignedVec, Archive, Archived, ArchivedMetadata, ArchivePointee, ArchiveUnsized, FixedUsize, RelPtr, Serialize, SerializeUnsized, }; // We're going to be dealing mostly with blocks that have a trailing slice pub struct Block<H, T: ?Sized> { head: H, tail: T, } impl<H, T> Pointee for Block<H, [T]> { type Metadata = usize; } // For blocks with trailing slices, we need to store the length of the slice // in the metadata. pub struct BlockSliceMetadata { len: Archived<usize>, } // ArchivePointee is automatically derived for sized types because pointers // to sized types don't need to store any extra information. Because we're // making an unsized block, we need to define what metadata gets stored with // our data pointer. impl<H, T> ArchivePointee for Block<H, [T]> { // This is the extra data that needs to get stored for blocks with // trailing slices type ArchivedMetadata = BlockSliceMetadata; // We need to be able to turn our archived metadata into regular // metadata for our type fn pointer_metadata( archived: &Self::ArchivedMetadata ) -> <Self as Pointee>::Metadata { from_archived!(archived.len) as usize } } // We're implementing ArchiveUnsized for just Block<H, [T]>. We can still // implement Archive for blocks with sized tails and they won't conflict. impl<H: Archive, T: Archive> ArchiveUnsized for Block<H, [T]> { // We'll reuse our block type as our archived type. type Archived = Block<Archived<H>, [Archived<T>]>; // This is where we'd put any resolve data for our metadata. // Most of the time, this can just be () because most metadata is Copy, // but the option is there if you need it. type MetadataResolver = (); // Here's where we make the metadata for our pointer. // This also gets the position and resolver for the metadata, but we // don't need it in this case. unsafe fn resolve_metadata( &self, _: usize, _: Self::MetadataResolver, out: *mut ArchivedMetadata<Self>, ) { unsafe { out.write(BlockSliceMetadata { len: to_archived!(self.tail.len() as FixedUsize), }); } } } // The bounds we use on our serializer type indicate that we need basic // serializer capabilities, and then whatever capabilities our head and tail // types need to serialize themselves. impl< H: Serialize<S>, T: Serialize<S>, S: Serializer + ?Sized > SerializeUnsized<S> for Block<H, [T]> { // This is where we construct our unsized type in the serializer fn serialize_unsized( &self, serializer: &mut S ) -> Result<usize, S::Error> { // First, we archive the head and all the tails. This will make sure // that when we finally build our block, we don't accidentally mess // up the structure with serialized dependencies. let head_resolver = self.head.serialize(serializer)?; let mut resolvers = Vec::new(); for tail in self.tail.iter() { resolvers.push(tail.serialize(serializer)?); } // Now we align our serializer for our archived type and write it. // We can't align for unsized types so we treat the trailing slice // like an array of 0 length for now. serializer.align_for::<Block<Archived<H>, [Archived<T>; 0]>>()?; let result = unsafe { serializer.resolve_aligned(&self.head, head_resolver)? }; serializer.align_for::<Archived<T>>()?; for (item, resolver) in self.tail.iter().zip(resolvers.drain(..)) { unsafe { serializer.resolve_aligned(item, resolver)?; } } Ok(result) } // This is where we serialize the metadata for our type. In this case, // we do all the work in resolve and don't need to do anything here. fn serialize_metadata( &self, serializer: &mut S ) -> Result<Self::MetadataResolver, S::Error> { Ok(()) } } let value = Block { head: "Numbers 1-4".to_string(), tail: [1, 2, 3, 4], }; // We have a Block<String, [i32; 4]> but we want to it to be a // Block<String, [i32]>, so we need to do more pointer transmutation let ptr = (&value as *const Block<String, [i32; 4]>).cast::<()>(); let unsized_value = unsafe { &*transmute::<(*const (), usize), *const Block<String, [i32]>>((ptr, 4)) }; let mut serializer = AlignedSerializer::new(AlignedVec::new()); let pos = serializer.serialize_unsized_value(unsized_value) .expect("failed to archive block"); let buf = serializer.into_inner(); let archived_ref = unsafe { archived_unsized_value::<Block<String, [i32]>>(buf.as_slice(), pos) }; assert_eq!(archived_ref.head, "Numbers 1-4"); assert_eq!(archived_ref.tail.len(), 4); assert_eq!(archived_ref.tail, [1, 2, 3, 4]);
Associated Types
type Archived: ArchivePointee + ?Sized
type Archived: ArchivePointee + ?Sized
The archived counterpart of this type. Unlike Archive
, it may be unsized.
The resolver for the metadata of this type.
Required methods
unsafe fn resolve_metadata(
&self,
pos: usize,
resolver: Self::MetadataResolver,
out: *mut ArchivedMetadata<Self>
)
unsafe fn resolve_metadata(
&self,
pos: usize,
resolver: Self::MetadataResolver,
out: *mut ArchivedMetadata<Self>
)
Creates the archived version of the metadata for this value at the given position and writes it to the given output.
The output should be initialized field-by-field rather than by writing a whole struct. This is because performing a typed copy will set all of the padding bytes to uninitialized, but they must remain whatever value they currently have. This is so that uninitialized memory doesn’t get leaked to the final archive.
Safety
pos
must be the position ofout
within the archiveresolver
must be the result of serializing this object’s metadata
Provided methods
unsafe fn resolve_unsized(
&self,
from: usize,
to: usize,
resolver: Self::MetadataResolver,
out: *mut RelPtr<Self::Archived>
)
unsafe fn resolve_unsized(
&self,
from: usize,
to: usize,
resolver: Self::MetadataResolver,
out: *mut RelPtr<Self::Archived>
)
Resolves a relative pointer to this value with the given from
and to
and writes it to
the given output.
The output should be initialized field-by-field rather than by writing a whole struct. This is because performing a typed copy will set all of the padding bytes to uninitialized, but they must remain whatever value they currently have. This is so that uninitialized memory doesn’t get leaked to the final archive.
Safety
from
must be the position ofout
within the archiveto
must be the position of someSelf::Archived
within the archiveresolver
must be the result of serializing this object
Implementations on Foreign Types
type MetadataResolver = ()
unsafe fn resolve_metadata(
&self,
_: usize,
_: Self::MetadataResolver,
out: *mut ArchivedMetadata<Self>
)
str
type MetadataResolver = ()
unsafe fn resolve_metadata(
&self,
_: usize,
_: Self::MetadataResolver,
out: *mut ArchivedMetadata<Self>
)
type MetadataResolver = ()
unsafe fn resolve_metadata(
&self,
_: usize,
_: Self::MetadataResolver,
out: *mut ArchivedMetadata<Self>
)