vendor/zerovec/src/ule/encode.rs - toolchain/rustc - Git at Google

 // This file is part of ICU4X. For terms of use, please see the file
 // called LICENSE at the top level of the ICU4X source tree
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).

 use crate::ule::*;
 use crate::varzerovec::VarZeroVecFormat;
 use crate::{VarZeroSlice, VarZeroVec, ZeroSlice, ZeroVec};
 use alloc::borrow::{Cow, ToOwned};
 use alloc::boxed::Box;
 use alloc::string::String;
 use alloc::vec::Vec;
 use core::mem;

 /// Allows types to be encoded as VarULEs. This is highly useful for implementing VarULE on
 /// custom DSTs where the type cannot be obtained as a reference to some other type.
 ///
 /// [`Self::encode_var_ule_as_slices()`] should be implemented by providing an encoded slice for each field
 /// of the VarULE type to the callback, in order. For an implementation to be safe, the slices
 /// to the callback must, when concatenated, be a valid instance of the VarULE type.
 ///
 /// See the [custom VarULEdocumentation](crate::ule::custom) for examples.
 ///
 /// [`Self::encode_var_ule_as_slices()`] is only used to provide default implementations for [`Self::encode_var_ule_write()`]
 /// and [`Self::encode_var_ule_len()`]. If you override the default implementations it is totally valid to
 /// replace [`Self::encode_var_ule_as_slices()`]'s body with `unreachable!()`. This can be done for cases where
 /// it is not possible to implement [`Self::encode_var_ule_as_slices()`] but the other methods still work.
 ///
 /// A typical implementation will take each field in the order found in the [`VarULE`] type,
 /// convert it to ULE, call [`ULE::as_byte_slice()`] on them, and pass the slices to `cb` in order.
 /// A trailing [`ZeroVec`](crate::ZeroVec) or [`VarZeroVec`](crate::VarZeroVec) can have their underlying
 /// byte representation passed through.
 ///
 /// In case the compiler is not optimizing [`Self::encode_var_ule_len()`], it can be overridden. A typical
 /// implementation will add up the sizes of each field on the [`VarULE`] type and then add in the byte length of the
 /// dynamically-sized part.
 ///
 /// # Safety
 ///
 /// The safety invariants of [`Self::encode_var_ule_as_slices()`] are:
 /// - It must call `cb` (only once)
 /// - The slices passed to `cb`, if concatenated, should be a valid instance of the `T` [`VarULE`] type
 ///   (i.e. if fed to [`VarULE::validate_byte_slice()`] they must produce a successful result)
 /// - It must return the return value of `cb` to the caller
 ///
 /// One or more of [`Self::encode_var_ule_len()`] and [`Self::encode_var_ule_write()`] may be provided.
 /// If both are, then `zerovec` code is guaranteed to not call [`Self::encode_var_ule_as_slices()`], and it may be replaced
 /// with `unreachable!()`.
 ///
 /// The safety invariants of [`Self::encode_var_ule_len()`] are:
 /// - It must return the length of the corresponding VarULE type
 ///
 /// The safety invariants of [`Self::encode_var_ule_write()`] are:
 /// - The slice written to `dst` must be a valid instance of the `T` [`VarULE`] type
 pub unsafe trait EncodeAsVarULE<T: VarULE + ?Sized> {
     /// Calls `cb` with a piecewise list of byte slices that when concatenated
     /// produce the memory pattern of the corresponding instance of `T`.
     ///
     /// Do not call this function directly; instead use the other two. Some implementors
     /// may define this function to panic.
     fn encode_var_ule_as_slices<R>(&self, cb: impl FnOnce(&[&[u8]]) -> R) -> R;

     /// Return the length, in bytes, of the corresponding [`VarULE`] type
     fn encode_var_ule_len(&self) -> usize {
         self.encode_var_ule_as_slices(|slices| slices.iter().map(|s| s.len()).sum())
     }

     /// Write the corresponding [`VarULE`] type to the `dst` buffer. `dst` should
     /// be the size of [`Self::encode_var_ule_len()`]
     fn encode_var_ule_write(&self, mut dst: &mut [u8]) {
         debug_assert_eq!(self.encode_var_ule_len(), dst.len());
         self.encode_var_ule_as_slices(move |slices| {
             #[allow(clippy::indexing_slicing)] // by debug_assert
             for slice in slices {
                 dst[..slice.len()].copy_from_slice(slice);
                 dst = &mut dst[slice.len()..];
             }
         });
     }
 }

 /// Given an [`EncodeAsVarULE`] type `S`, encode it into a `Box<T>`
 ///
 /// This is primarily useful for generating `Deserialize` impls for VarULE types
 pub fn encode_varule_to_box<S: EncodeAsVarULE<T>, T: VarULE + ?Sized>(x: &S) -> Box<T> {
     let mut vec: Vec<u8> = Vec::new();
     // zero-fill the vector to avoid uninitialized data UB
     vec.resize(x.encode_var_ule_len(), 0);
     x.encode_var_ule_write(&mut vec);
     let boxed = vec.into_boxed_slice();
     unsafe {
         // Safety: `ptr` is a box, and `T` is a VarULE which guarantees it has the same memory layout as `[u8]`
         // and can be recouped via from_byte_slice_unchecked()
         let ptr: *mut T = T::from_byte_slice_unchecked(&boxed) as *const T as *mut T;
         mem::forget(boxed);

         // Safety: we can construct an owned version since we have mem::forgotten the older owner
         Box::from_raw(ptr)
     }
 }

 unsafe impl<T: VarULE + ?Sized> EncodeAsVarULE<T> for T {
     fn encode_var_ule_as_slices<R>(&self, cb: impl FnOnce(&[&[u8]]) -> R) -> R {
         cb(&[T::as_byte_slice(self)])
     }
 }

 unsafe impl<T: VarULE + ?Sized> EncodeAsVarULE<T> for &'_ T {
     fn encode_var_ule_as_slices<R>(&self, cb: impl FnOnce(&[&[u8]]) -> R) -> R {
         cb(&[T::as_byte_slice(self)])
     }
 }

 unsafe impl<T: VarULE + ?Sized> EncodeAsVarULE<T> for Cow<'_, T>
 where
     T: ToOwned,
 {
     fn encode_var_ule_as_slices<R>(&self, cb: impl FnOnce(&[&[u8]]) -> R) -> R {
         cb(&[T::as_byte_slice(self.as_ref())])
     }
 }

 unsafe impl<T: VarULE + ?Sized> EncodeAsVarULE<T> for Box<T> {
     fn encode_var_ule_as_slices<R>(&self, cb: impl FnOnce(&[&[u8]]) -> R) -> R {
         cb(&[T::as_byte_slice(self)])
     }
 }

 unsafe impl EncodeAsVarULE<str> for String {
     fn encode_var_ule_as_slices<R>(&self, cb: impl FnOnce(&[&[u8]]) -> R) -> R {
         cb(&[self.as_bytes()])
     }
 }

 // Note: This impl could technically use `T: AsULE`, but we want users to prefer `ZeroSlice<T>`
 // for cases where T is not a ULE. Therefore, we can use the more efficient `memcpy` impl here.
 unsafe impl<T> EncodeAsVarULE<[T]> for Vec<T>
 where
     T: ULE,
 {
     fn encode_var_ule_as_slices<R>(&self, cb: impl FnOnce(&[&[u8]]) -> R) -> R {
         cb(&[<[T] as VarULE>::as_byte_slice(self)])
     }
 }

 unsafe impl<T> EncodeAsVarULE<ZeroSlice<T>> for &'_ [T]
 where
     T: AsULE + 'static,
 {
     fn encode_var_ule_as_slices<R>(&self, _: impl FnOnce(&[&[u8]]) -> R) -> R {
         // unnecessary if the other two are implemented
         unreachable!()
     }

     #[inline]
     fn encode_var_ule_len(&self) -> usize {
         self.len() * core::mem::size_of::<T::ULE>()
     }

     fn encode_var_ule_write(&self, dst: &mut [u8]) {
         #[allow(non_snake_case)]
         let S = core::mem::size_of::<T::ULE>();
         debug_assert_eq!(self.len() * S, dst.len());
         for (item, ref mut chunk) in self.iter().zip(dst.chunks_mut(S)) {
             let ule = item.to_unaligned();
             chunk.copy_from_slice(ULE::as_byte_slice(core::slice::from_ref(&ule)));
         }
     }
 }

 unsafe impl<T> EncodeAsVarULE<ZeroSlice<T>> for Vec<T>
 where
     T: AsULE + 'static,
 {
     fn encode_var_ule_as_slices<R>(&self, _: impl FnOnce(&[&[u8]]) -> R) -> R {
         // unnecessary if the other two are implemented
         unreachable!()
     }

     #[inline]
     fn encode_var_ule_len(&self) -> usize {
         self.as_slice().encode_var_ule_len()
     }

     #[inline]
     fn encode_var_ule_write(&self, dst: &mut [u8]) {
         self.as_slice().encode_var_ule_write(dst)
     }
 }

 unsafe impl<T> EncodeAsVarULE<ZeroSlice<T>> for ZeroVec<'_, T>
 where
     T: AsULE + 'static,
 {
     fn encode_var_ule_as_slices<R>(&self, _: impl FnOnce(&[&[u8]]) -> R) -> R {
         // unnecessary if the other two are implemented
         unreachable!()
     }

     #[inline]
     fn encode_var_ule_len(&self) -> usize {
         self.as_bytes().len()
     }

     fn encode_var_ule_write(&self, dst: &mut [u8]) {
         debug_assert_eq!(self.as_bytes().len(), dst.len());
         dst.copy_from_slice(self.as_bytes());
     }
 }

 unsafe impl<T, E, F> EncodeAsVarULE<VarZeroSlice<T, F>> for &'_ [E]
 where
     T: VarULE + ?Sized,
     E: EncodeAsVarULE<T>,
     F: VarZeroVecFormat,
 {
     fn encode_var_ule_as_slices<R>(&self, _: impl FnOnce(&[&[u8]]) -> R) -> R {
         // unnecessary if the other two are implemented
         unimplemented!()
     }

     #[allow(clippy::unwrap_used)] // TODO(#1410): Rethink length errors in VZV.
     fn encode_var_ule_len(&self) -> usize {
         crate::varzerovec::components::compute_serializable_len::<T, E, F>(self).unwrap() as usize
     }

     fn encode_var_ule_write(&self, dst: &mut [u8]) {
         crate::varzerovec::components::write_serializable_bytes::<T, E, F>(self, dst)
     }
 }

 unsafe impl<T, E, F> EncodeAsVarULE<VarZeroSlice<T, F>> for Vec<E>
 where
     T: VarULE + ?Sized,
     E: EncodeAsVarULE<T>,
     F: VarZeroVecFormat,
 {
     fn encode_var_ule_as_slices<R>(&self, _: impl FnOnce(&[&[u8]]) -> R) -> R {
         // unnecessary if the other two are implemented
         unreachable!()
     }

     #[inline]
     fn encode_var_ule_len(&self) -> usize {
         <_ as EncodeAsVarULE<VarZeroSlice<T, F>>>::encode_var_ule_len(&self.as_slice())
     }

     #[inline]
     fn encode_var_ule_write(&self, dst: &mut [u8]) {
         <_ as EncodeAsVarULE<VarZeroSlice<T, F>>>::encode_var_ule_write(&self.as_slice(), dst)
     }
 }

 unsafe impl<T, F> EncodeAsVarULE<VarZeroSlice<T, F>> for VarZeroVec<'_, T, F>
 where
     T: VarULE + ?Sized,
     F: VarZeroVecFormat,
 {
     fn encode_var_ule_as_slices<R>(&self, _: impl FnOnce(&[&[u8]]) -> R) -> R {
         // unnecessary if the other two are implemented
         unreachable!()
     }

     #[inline]
     fn encode_var_ule_len(&self) -> usize {
         self.as_bytes().len()
     }

     #[inline]
     fn encode_var_ule_write(&self, dst: &mut [u8]) {
         debug_assert_eq!(self.as_bytes().len(), dst.len());
         dst.copy_from_slice(self.as_bytes());
     }
 }

 #[cfg(test)]
 mod test {
     use super::*;

     const STRING_ARRAY: [&str; 2] = ["hello", "world"];

     const STRING_SLICE: &[&str] = &STRING_ARRAY;

     const U8_ARRAY: [u8; 8] = [0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07];

     const U8_2D_ARRAY: [&[u8]; 2] = [&U8_ARRAY, &U8_ARRAY];

     const U8_2D_SLICE: &[&[u8]] = &[&U8_ARRAY, &U8_ARRAY];

     const U8_3D_ARRAY: [&[&[u8]]; 2] = [U8_2D_SLICE, U8_2D_SLICE];

     const U8_3D_SLICE: &[&[&[u8]]] = &[U8_2D_SLICE, U8_2D_SLICE];

     const U32_ARRAY: [u32; 4] = [0x00010203, 0x04050607, 0x08090A0B, 0x0C0D0E0F];

     const U32_2D_ARRAY: [&[u32]; 2] = [&U32_ARRAY, &U32_ARRAY];

     const U32_2D_SLICE: &[&[u32]] = &[&U32_ARRAY, &U32_ARRAY];

     const U32_3D_ARRAY: [&[&[u32]]; 2] = [U32_2D_SLICE, U32_2D_SLICE];

     const U32_3D_SLICE: &[&[&[u32]]] = &[U32_2D_SLICE, U32_2D_SLICE];

     #[test]
     fn test_vzv_from() {
         type VZV<'a, T> = VarZeroVec<'a, T>;
         type ZS<T> = ZeroSlice<T>;
         type VZS<T> = VarZeroSlice<T>;

         let u8_zerovec: ZeroVec<u8> = ZeroVec::from_slice_or_alloc(&U8_ARRAY);
         let u8_2d_zerovec: [ZeroVec<u8>; 2] = [u8_zerovec.clone(), u8_zerovec.clone()];
         let u8_2d_vec: Vec<Vec<u8>> = vec![U8_ARRAY.into(), U8_ARRAY.into()];
         let u8_3d_vec: Vec<Vec<Vec<u8>>> = vec![u8_2d_vec.clone(), u8_2d_vec.clone()];

         let u32_zerovec: ZeroVec<u32> = ZeroVec::from_slice_or_alloc(&U32_ARRAY);
         let u32_2d_zerovec: [ZeroVec<u32>; 2] = [u32_zerovec.clone(), u32_zerovec.clone()];
         let u32_2d_vec: Vec<Vec<u32>> = vec![U32_ARRAY.into(), U32_ARRAY.into()];
         let u32_3d_vec: Vec<Vec<Vec<u32>>> = vec![u32_2d_vec.clone(), u32_2d_vec.clone()];

         let a: VZV<str> = VarZeroVec::from(&STRING_ARRAY);
         let b: VZV<str> = VarZeroVec::from(STRING_SLICE);
         let c: VZV<str> = VarZeroVec::from(&Vec::from(STRING_SLICE));
         assert_eq!(a, STRING_SLICE);
         assert_eq!(a, b);
         assert_eq!(a, c);

         let a: VZV<[u8]> = VarZeroVec::from(&U8_2D_ARRAY);
         let b: VZV<[u8]> = VarZeroVec::from(U8_2D_SLICE);
         let c: VZV<[u8]> = VarZeroVec::from(&u8_2d_vec);
         assert_eq!(a, U8_2D_SLICE);
         assert_eq!(a, b);
         assert_eq!(a, c);
         let u8_3d_vzv_brackets = &[a.clone(), a.clone()];

         let a: VZV<ZS<u8>> = VarZeroVec::from(&U8_2D_ARRAY);
         let b: VZV<ZS<u8>> = VarZeroVec::from(U8_2D_SLICE);
         let c: VZV<ZS<u8>> = VarZeroVec::from(&u8_2d_vec);
         let d: VZV<ZS<u8>> = VarZeroVec::from(&u8_2d_zerovec);
         assert_eq!(a, U8_2D_SLICE);
         assert_eq!(a, b);
         assert_eq!(a, c);
         assert_eq!(a, d);
         let u8_3d_vzv_zeroslice = &[a.clone(), a.clone()];

         let a: VZV<VZS<[u8]>> = VarZeroVec::from(&U8_3D_ARRAY);
         let b: VZV<VZS<[u8]>> = VarZeroVec::from(U8_3D_SLICE);
         let c: VZV<VZS<[u8]>> = VarZeroVec::from(&u8_3d_vec);
         let d: VZV<VZS<[u8]>> = VarZeroVec::from(u8_3d_vzv_brackets);
         assert_eq!(
             a.iter()
                 .map(|x| x.iter().map(|y| y.to_vec()).collect::<Vec<Vec<u8>>>())
                 .collect::<Vec<Vec<Vec<u8>>>>(),
             u8_3d_vec
         );
         assert_eq!(a, b);
         assert_eq!(a, c);
         assert_eq!(a, d);

         let a: VZV<VZS<ZS<u8>>> = VarZeroVec::from(&U8_3D_ARRAY);
         let b: VZV<VZS<ZS<u8>>> = VarZeroVec::from(U8_3D_SLICE);
         let c: VZV<VZS<ZS<u8>>> = VarZeroVec::from(&u8_3d_vec);
         let d: VZV<VZS<ZS<u8>>> = VarZeroVec::from(u8_3d_vzv_zeroslice);
         assert_eq!(
             a.iter()
                 .map(|x| x
                     .iter()
                     .map(|y| y.iter().collect::<Vec<u8>>())
                     .collect::<Vec<Vec<u8>>>())
                 .collect::<Vec<Vec<Vec<u8>>>>(),
             u8_3d_vec
         );
         assert_eq!(a, b);
         assert_eq!(a, c);
         assert_eq!(a, d);

         let a: VZV<ZS<u32>> = VarZeroVec::from(&U32_2D_ARRAY);
         let b: VZV<ZS<u32>> = VarZeroVec::from(U32_2D_SLICE);
         let c: VZV<ZS<u32>> = VarZeroVec::from(&u32_2d_vec);
         let d: VZV<ZS<u32>> = VarZeroVec::from(&u32_2d_zerovec);
         assert_eq!(a, u32_2d_zerovec);
         assert_eq!(a, b);
         assert_eq!(a, c);
         assert_eq!(a, d);
         let u32_3d_vzv = &[a.clone(), a.clone()];

         let a: VZV<VZS<ZS<u32>>> = VarZeroVec::from(&U32_3D_ARRAY);
         let b: VZV<VZS<ZS<u32>>> = VarZeroVec::from(U32_3D_SLICE);
         let c: VZV<VZS<ZS<u32>>> = VarZeroVec::from(&u32_3d_vec);
         let d: VZV<VZS<ZS<u32>>> = VarZeroVec::from(u32_3d_vzv);
         assert_eq!(
             a.iter()
                 .map(|x| x
                     .iter()
                     .map(|y| y.iter().collect::<Vec<u32>>())
                     .collect::<Vec<Vec<u32>>>())
                 .collect::<Vec<Vec<Vec<u32>>>>(),
             u32_3d_vec
         );
         assert_eq!(a, b);
         assert_eq!(a, c);
         assert_eq!(a, d);
     }
 }
	// This file is part of ICU4X. For terms of use, please see the file
	// called LICENSE at the top level of the ICU4X source tree
	// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).

	use crate::ule::*;
	use crate::varzerovec::VarZeroVecFormat;
	use crate::{VarZeroSlice, VarZeroVec, ZeroSlice, ZeroVec};
	use alloc::borrow::{Cow, ToOwned};
	use alloc::boxed::Box;
	use alloc::string::String;
	use alloc::vec::Vec;
	use core::mem;

	/// Allows types to be encoded as VarULEs. This is highly useful for implementing VarULE on
	/// custom DSTs where the type cannot be obtained as a reference to some other type.
	///
	/// [`Self::encode_var_ule_as_slices()`] should be implemented by providing an encoded slice for each field
	/// of the VarULE type to the callback, in order. For an implementation to be safe, the slices
	/// to the callback must, when concatenated, be a valid instance of the VarULE type.
	///
	/// See the [custom VarULEdocumentation](crate::ule::custom) for examples.
	///
	/// [`Self::encode_var_ule_as_slices()`] is only used to provide default implementations for [`Self::encode_var_ule_write()`]
	/// and [`Self::encode_var_ule_len()`]. If you override the default implementations it is totally valid to
	/// replace [`Self::encode_var_ule_as_slices()`]'s body with `unreachable!()`. This can be done for cases where
	/// it is not possible to implement [`Self::encode_var_ule_as_slices()`] but the other methods still work.
	///
	/// A typical implementation will take each field in the order found in the [`VarULE`] type,
	/// convert it to ULE, call [`ULE::as_byte_slice()`] on them, and pass the slices to `cb` in order.
	/// A trailing [`ZeroVec`](crate::ZeroVec) or [`VarZeroVec`](crate::VarZeroVec) can have their underlying
	/// byte representation passed through.
	///
	/// In case the compiler is not optimizing [`Self::encode_var_ule_len()`], it can be overridden. A typical
	/// implementation will add up the sizes of each field on the [`VarULE`] type and then add in the byte length of the
	/// dynamically-sized part.
	///
	/// # Safety
	///
	/// The safety invariants of [`Self::encode_var_ule_as_slices()`] are:
	/// - It must call `cb` (only once)
	/// - The slices passed to `cb`, if concatenated, should be a valid instance of the `T` [`VarULE`] type
	/// (i.e. if fed to [`VarULE::validate_byte_slice()`] they must produce a successful result)
	/// - It must return the return value of `cb` to the caller
	///
	/// One or more of [`Self::encode_var_ule_len()`] and [`Self::encode_var_ule_write()`] may be provided.
	/// If both are, then `zerovec` code is guaranteed to not call [`Self::encode_var_ule_as_slices()`], and it may be replaced
	/// with `unreachable!()`.
	///
	/// The safety invariants of [`Self::encode_var_ule_len()`] are:
	/// - It must return the length of the corresponding VarULE type
	///
	/// The safety invariants of [`Self::encode_var_ule_write()`] are:
	/// - The slice written to `dst` must be a valid instance of the `T` [`VarULE`] type
	pub unsafe trait EncodeAsVarULE<T: VarULE + ?Sized> {
	/// Calls `cb` with a piecewise list of byte slices that when concatenated
	/// produce the memory pattern of the corresponding instance of `T`.
	///
	/// Do not call this function directly; instead use the other two. Some implementors
	/// may define this function to panic.
	fn encode_var_ule_as_slices<R>(&self, cb: impl FnOnce(&[&[u8]]) -> R) -> R;

	/// Return the length, in bytes, of the corresponding [`VarULE`] type
	fn encode_var_ule_len(&self) -> usize {
	self.encode_var_ule_as_slices(\|slices\| slices.iter().map(\|s\| s.len()).sum())
	}

	/// Write the corresponding [`VarULE`] type to the `dst` buffer. `dst` should
	/// be the size of [`Self::encode_var_ule_len()`]
	fn encode_var_ule_write(&self, mut dst: &mut [u8]) {
	debug_assert_eq!(self.encode_var_ule_len(), dst.len());
	self.encode_var_ule_as_slices(move \|slices\| {
	#[allow(clippy::indexing_slicing)] // by debug_assert
	for slice in slices {
	dst[..slice.len()].copy_from_slice(slice);
	dst = &mut dst[slice.len()..];
	}
	});
	}
	}

	/// Given an [`EncodeAsVarULE`] type `S`, encode it into a `Box<T>`
	///
	/// This is primarily useful for generating `Deserialize` impls for VarULE types
	pub fn encode_varule_to_box<S: EncodeAsVarULE<T>, T: VarULE + ?Sized>(x: &S) -> Box<T> {
	let mut vec: Vec<u8> = Vec::new();
	// zero-fill the vector to avoid uninitialized data UB
	vec.resize(x.encode_var_ule_len(), 0);
	x.encode_var_ule_write(&mut vec);
	let boxed = vec.into_boxed_slice();
	unsafe {
	// Safety: `ptr` is a box, and `T` is a VarULE which guarantees it has the same memory layout as `[u8]`
	// and can be recouped via from_byte_slice_unchecked()
	let ptr: mut T = T::from_byte_slice_unchecked(&boxed) as const T as *mut T;
	mem::forget(boxed);

	// Safety: we can construct an owned version since we have mem::forgotten the older owner
	Box::from_raw(ptr)
	}
	}

	unsafe impl<T: VarULE + ?Sized> EncodeAsVarULE<T> for T {
	fn encode_var_ule_as_slices<R>(&self, cb: impl FnOnce(&[&[u8]]) -> R) -> R {
	cb(&[T::as_byte_slice(self)])
	}
	}

	unsafe impl<T: VarULE + ?Sized> EncodeAsVarULE<T> for &'_ T {
	fn encode_var_ule_as_slices<R>(&self, cb: impl FnOnce(&[&[u8]]) -> R) -> R {
	cb(&[T::as_byte_slice(self)])
	}
	}

	unsafe impl<T: VarULE + ?Sized> EncodeAsVarULE<T> for Cow<'_, T>
	where
	T: ToOwned,
	{
	fn encode_var_ule_as_slices<R>(&self, cb: impl FnOnce(&[&[u8]]) -> R) -> R {
	cb(&[T::as_byte_slice(self.as_ref())])
	}
	}

	unsafe impl<T: VarULE + ?Sized> EncodeAsVarULE<T> for Box<T> {
	fn encode_var_ule_as_slices<R>(&self, cb: impl FnOnce(&[&[u8]]) -> R) -> R {
	cb(&[T::as_byte_slice(self)])
	}
	}

	unsafe impl EncodeAsVarULE<str> for String {
	fn encode_var_ule_as_slices<R>(&self, cb: impl FnOnce(&[&[u8]]) -> R) -> R {
	cb(&[self.as_bytes()])
	}
	}

	// Note: This impl could technically use `T: AsULE`, but we want users to prefer `ZeroSlice<T>`
	// for cases where T is not a ULE. Therefore, we can use the more efficient `memcpy` impl here.
	unsafe impl<T> EncodeAsVarULE<[T]> for Vec<T>
	where
	T: ULE,
	{
	fn encode_var_ule_as_slices<R>(&self, cb: impl FnOnce(&[&[u8]]) -> R) -> R {
	cb(&[<[T] as VarULE>::as_byte_slice(self)])
	}
	}

	unsafe impl<T> EncodeAsVarULE<ZeroSlice<T>> for &'_ [T]
	where
	T: AsULE + 'static,
	{
	fn encode_var_ule_as_slices<R>(&self, _: impl FnOnce(&[&[u8]]) -> R) -> R {
	// unnecessary if the other two are implemented
	unreachable!()
	}

	#[inline]
	fn encode_var_ule_len(&self) -> usize {
	self.len() * core::mem::size_of::<T::ULE>()
	}

	fn encode_var_ule_write(&self, dst: &mut [u8]) {
	#[allow(non_snake_case)]
	let S = core::mem::size_of::<T::ULE>();
	debug_assert_eq!(self.len() * S, dst.len());
	for (item, ref mut chunk) in self.iter().zip(dst.chunks_mut(S)) {
	let ule = item.to_unaligned();
	chunk.copy_from_slice(ULE::as_byte_slice(core::slice::from_ref(&ule)));
	}
	}
	}

	unsafe impl<T> EncodeAsVarULE<ZeroSlice<T>> for Vec<T>
	where
	T: AsULE + 'static,
	{
	fn encode_var_ule_as_slices<R>(&self, _: impl FnOnce(&[&[u8]]) -> R) -> R {
	// unnecessary if the other two are implemented
	unreachable!()
	}

	#[inline]
	fn encode_var_ule_len(&self) -> usize {
	self.as_slice().encode_var_ule_len()
	}

	#[inline]
	fn encode_var_ule_write(&self, dst: &mut [u8]) {
	self.as_slice().encode_var_ule_write(dst)
	}
	}

	unsafe impl<T> EncodeAsVarULE<ZeroSlice<T>> for ZeroVec<'_, T>
	where
	T: AsULE + 'static,
	{
	fn encode_var_ule_as_slices<R>(&self, _: impl FnOnce(&[&[u8]]) -> R) -> R {
	// unnecessary if the other two are implemented
	unreachable!()
	}

	#[inline]
	fn encode_var_ule_len(&self) -> usize {
	self.as_bytes().len()
	}

	fn encode_var_ule_write(&self, dst: &mut [u8]) {
	debug_assert_eq!(self.as_bytes().len(), dst.len());
	dst.copy_from_slice(self.as_bytes());
	}
	}

	unsafe impl<T, E, F> EncodeAsVarULE<VarZeroSlice<T, F>> for &'_ [E]
	where
	T: VarULE + ?Sized,
	E: EncodeAsVarULE<T>,
	F: VarZeroVecFormat,
	{
	fn encode_var_ule_as_slices<R>(&self, _: impl FnOnce(&[&[u8]]) -> R) -> R {
	// unnecessary if the other two are implemented
	unimplemented!()
	}

	#[allow(clippy::unwrap_used)] // TODO(#1410): Rethink length errors in VZV.
	fn encode_var_ule_len(&self) -> usize {
	crate::varzerovec::components::compute_serializable_len::<T, E, F>(self).unwrap() as usize
	}

	fn encode_var_ule_write(&self, dst: &mut [u8]) {
	crate::varzerovec::components::write_serializable_bytes::<T, E, F>(self, dst)
	}
	}

	unsafe impl<T, E, F> EncodeAsVarULE<VarZeroSlice<T, F>> for Vec<E>
	where
	T: VarULE + ?Sized,
	E: EncodeAsVarULE<T>,
	F: VarZeroVecFormat,
	{
	fn encode_var_ule_as_slices<R>(&self, _: impl FnOnce(&[&[u8]]) -> R) -> R {
	// unnecessary if the other two are implemented
	unreachable!()
	}

	#[inline]
	fn encode_var_ule_len(&self) -> usize {
	<_ as EncodeAsVarULE<VarZeroSlice<T, F>>>::encode_var_ule_len(&self.as_slice())
	}

	#[inline]
	fn encode_var_ule_write(&self, dst: &mut [u8]) {
	<_ as EncodeAsVarULE<VarZeroSlice<T, F>>>::encode_var_ule_write(&self.as_slice(), dst)
	}
	}

	unsafe impl<T, F> EncodeAsVarULE<VarZeroSlice<T, F>> for VarZeroVec<'_, T, F>
	where
	T: VarULE + ?Sized,
	F: VarZeroVecFormat,
	{
	fn encode_var_ule_as_slices<R>(&self, _: impl FnOnce(&[&[u8]]) -> R) -> R {
	// unnecessary if the other two are implemented
	unreachable!()
	}

	#[inline]
	fn encode_var_ule_len(&self) -> usize {
	self.as_bytes().len()
	}

	#[inline]
	fn encode_var_ule_write(&self, dst: &mut [u8]) {
	debug_assert_eq!(self.as_bytes().len(), dst.len());
	dst.copy_from_slice(self.as_bytes());
	}
	}

	#[cfg(test)]
	mod test {
	use super::*;

	const STRING_ARRAY: [&str; 2] = ["hello", "world"];

	const STRING_SLICE: &[&str] = &STRING_ARRAY;

	const U8_ARRAY: [u8; 8] = [0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07];

	const U8_2D_ARRAY: [&[u8]; 2] = [&U8_ARRAY, &U8_ARRAY];

	const U8_2D_SLICE: &[&[u8]] = &[&U8_ARRAY, &U8_ARRAY];

	const U8_3D_ARRAY: [&[&[u8]]; 2] = [U8_2D_SLICE, U8_2D_SLICE];

	const U8_3D_SLICE: &[&[&[u8]]] = &[U8_2D_SLICE, U8_2D_SLICE];

	const U32_ARRAY: [u32; 4] = [0x00010203, 0x04050607, 0x08090A0B, 0x0C0D0E0F];

	const U32_2D_ARRAY: [&[u32]; 2] = [&U32_ARRAY, &U32_ARRAY];

	const U32_2D_SLICE: &[&[u32]] = &[&U32_ARRAY, &U32_ARRAY];

	const U32_3D_ARRAY: [&[&[u32]]; 2] = [U32_2D_SLICE, U32_2D_SLICE];

	const U32_3D_SLICE: &[&[&[u32]]] = &[U32_2D_SLICE, U32_2D_SLICE];

	#[test]
	fn test_vzv_from() {
	type VZV<'a, T> = VarZeroVec<'a, T>;
	type ZS<T> = ZeroSlice<T>;
	type VZS<T> = VarZeroSlice<T>;

	let u8_zerovec: ZeroVec<u8> = ZeroVec::from_slice_or_alloc(&U8_ARRAY);
	let u8_2d_zerovec: [ZeroVec<u8>; 2] = [u8_zerovec.clone(), u8_zerovec.clone()];
	let u8_2d_vec: Vec<Vec<u8>> = vec![U8_ARRAY.into(), U8_ARRAY.into()];
	let u8_3d_vec: Vec<Vec<Vec<u8>>> = vec![u8_2d_vec.clone(), u8_2d_vec.clone()];

	let u32_zerovec: ZeroVec<u32> = ZeroVec::from_slice_or_alloc(&U32_ARRAY);
	let u32_2d_zerovec: [ZeroVec<u32>; 2] = [u32_zerovec.clone(), u32_zerovec.clone()];
	let u32_2d_vec: Vec<Vec<u32>> = vec![U32_ARRAY.into(), U32_ARRAY.into()];
	let u32_3d_vec: Vec<Vec<Vec<u32>>> = vec![u32_2d_vec.clone(), u32_2d_vec.clone()];

	let a: VZV<str> = VarZeroVec::from(&STRING_ARRAY);
	let b: VZV<str> = VarZeroVec::from(STRING_SLICE);
	let c: VZV<str> = VarZeroVec::from(&Vec::from(STRING_SLICE));
	assert_eq!(a, STRING_SLICE);
	assert_eq!(a, b);
	assert_eq!(a, c);

	let a: VZV<[u8]> = VarZeroVec::from(&U8_2D_ARRAY);
	let b: VZV<[u8]> = VarZeroVec::from(U8_2D_SLICE);
	let c: VZV<[u8]> = VarZeroVec::from(&u8_2d_vec);
	assert_eq!(a, U8_2D_SLICE);
	assert_eq!(a, b);
	assert_eq!(a, c);
	let u8_3d_vzv_brackets = &[a.clone(), a.clone()];

	let a: VZV<ZS<u8>> = VarZeroVec::from(&U8_2D_ARRAY);
	let b: VZV<ZS<u8>> = VarZeroVec::from(U8_2D_SLICE);
	let c: VZV<ZS<u8>> = VarZeroVec::from(&u8_2d_vec);
	let d: VZV<ZS<u8>> = VarZeroVec::from(&u8_2d_zerovec);
	assert_eq!(a, U8_2D_SLICE);
	assert_eq!(a, b);
	assert_eq!(a, c);
	assert_eq!(a, d);
	let u8_3d_vzv_zeroslice = &[a.clone(), a.clone()];

	let a: VZV<VZS<[u8]>> = VarZeroVec::from(&U8_3D_ARRAY);
	let b: VZV<VZS<[u8]>> = VarZeroVec::from(U8_3D_SLICE);
	let c: VZV<VZS<[u8]>> = VarZeroVec::from(&u8_3d_vec);
	let d: VZV<VZS<[u8]>> = VarZeroVec::from(u8_3d_vzv_brackets);
	assert_eq!(
	a.iter()
	.map(\|x\| x.iter().map(\|y\| y.to_vec()).collect::<Vec<Vec<u8>>>())
	.collect::<Vec<Vec<Vec<u8>>>>(),
	u8_3d_vec
	);
	assert_eq!(a, b);
	assert_eq!(a, c);
	assert_eq!(a, d);

	let a: VZV<VZS<ZS<u8>>> = VarZeroVec::from(&U8_3D_ARRAY);
	let b: VZV<VZS<ZS<u8>>> = VarZeroVec::from(U8_3D_SLICE);
	let c: VZV<VZS<ZS<u8>>> = VarZeroVec::from(&u8_3d_vec);
	let d: VZV<VZS<ZS<u8>>> = VarZeroVec::from(u8_3d_vzv_zeroslice);
	assert_eq!(
	a.iter()
	.map(\|x\| x
	.iter()
	.map(\|y\| y.iter().collect::<Vec<u8>>())
	.collect::<Vec<Vec<u8>>>())
	.collect::<Vec<Vec<Vec<u8>>>>(),
	u8_3d_vec
	);
	assert_eq!(a, b);
	assert_eq!(a, c);
	assert_eq!(a, d);

	let a: VZV<ZS<u32>> = VarZeroVec::from(&U32_2D_ARRAY);
	let b: VZV<ZS<u32>> = VarZeroVec::from(U32_2D_SLICE);
	let c: VZV<ZS<u32>> = VarZeroVec::from(&u32_2d_vec);
	let d: VZV<ZS<u32>> = VarZeroVec::from(&u32_2d_zerovec);
	assert_eq!(a, u32_2d_zerovec);
	assert_eq!(a, b);
	assert_eq!(a, c);
	assert_eq!(a, d);
	let u32_3d_vzv = &[a.clone(), a.clone()];

	let a: VZV<VZS<ZS<u32>>> = VarZeroVec::from(&U32_3D_ARRAY);
	let b: VZV<VZS<ZS<u32>>> = VarZeroVec::from(U32_3D_SLICE);
	let c: VZV<VZS<ZS<u32>>> = VarZeroVec::from(&u32_3d_vec);
	let d: VZV<VZS<ZS<u32>>> = VarZeroVec::from(u32_3d_vzv);
	assert_eq!(
	a.iter()
	.map(\|x\| x
	.iter()
	.map(\|y\| y.iter().collect::<Vec<u32>>())
	.collect::<Vec<Vec<u32>>>())
	.collect::<Vec<Vec<Vec<u32>>>>(),
	u32_3d_vec
	);
	assert_eq!(a, b);
	assert_eq!(a, c);
	assert_eq!(a, d);
	}
	}