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Reverted 'static constraint on T in Vec<T> and [T; N] (#663)

This commit is contained in:
Trangar 2023-09-19 14:58:49 +02:00 committed by GitHub
parent 0d7e7950cb
commit 70fefd6dcc
3 changed files with 77 additions and 52 deletions
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51
src/de/impls.rs
View File

@ -8,7 +8,6 @@ use crate::{
impl_borrow_decode,
};
use core::{
any::TypeId,
cell::{Cell, RefCell},
num::{
NonZeroI128, NonZeroI16, NonZeroI32, NonZeroI64, NonZeroI8, NonZeroIsize, NonZeroU128,
@ -442,22 +441,24 @@ impl<'a, 'de: 'a> BorrowDecode<'de> for &'a str {
impl<T, const N: usize> Decode for [T; N]
where
T: Decode + Sized + 'static,
T: Decode + Sized,
{
fn decode<D: Decoder>(decoder: &mut D) -> Result<Self, DecodeError> {
decoder.claim_bytes_read(core::mem::size_of::<[T; N]>())?;
// Optimize for `[u8; N]`
if TypeId::of::<u8>() == TypeId::of::<T>() {
let mut buf = [0u8; N];
decoder.reader().read(&mut buf)?;
let ptr = &mut buf as *mut _ as *mut [T; N];
// TODO: we can't limit `T: 'static` because that would break other things
// but we want to have this optimization
// This will be another contendor for specialization implementation
// if TypeId::of::<u8>() == TypeId::of::<T>() {
// let mut buf = [0u8; N];
// decoder.reader().read(&mut buf)?;
// let ptr = &mut buf as *mut _ as *mut [T; N];
// Safety: we know that T is a u8, so it is perfectly safe to
// translate an array of u8 into an array of T
let res = unsafe { ptr.read() };
Ok(res)
} else {
// // Safety: we know that T is a u8, so it is perfectly safe to
// // translate an array of u8 into an array of T
// let res = unsafe { ptr.read() };
// Ok(res)
// }
let result = super::impl_core::collect_into_array(&mut (0..N).map(|_| {
// See the documentation on `unclaim_bytes_read` as to why we're doing this here
decoder.unclaim_bytes_read(core::mem::size_of::<T>());
@ -468,27 +469,28 @@ where
// So this unwrap should never occur
result.unwrap()
}
}
}
impl<'de, T, const N: usize> BorrowDecode<'de> for [T; N]
where
T: BorrowDecode<'de> + Sized + 'static,
T: BorrowDecode<'de> + Sized,
{
fn borrow_decode<D: BorrowDecoder<'de>>(decoder: &mut D) -> Result<Self, DecodeError> {
decoder.claim_bytes_read(core::mem::size_of::<[T; N]>())?;
// Optimize for `[u8; N]`
if TypeId::of::<u8>() == TypeId::of::<T>() {
let mut buf = [0u8; N];
decoder.reader().read(&mut buf)?;
let ptr = &mut buf as *mut _ as *mut [T; N];
// TODO: we can't limit `T: 'static` because that would break other things
// but we want to have this optimization
// This will be another contendor for specialization implementation
// if TypeId::of::<u8>() == TypeId::of::<T>() {
// let mut buf = [0u8; N];
// decoder.reader().read(&mut buf)?;
// let ptr = &mut buf as *mut _ as *mut [T; N];
// Safety: we know that T is a u8, so it is perfectly safe to
// translate an array of u8 into an array of T
let res = unsafe { ptr.read() };
Ok(res)
} else {
// // Safety: we know that T is a u8, so it is perfectly safe to
// // translate an array of u8 into an array of T
// let res = unsafe { ptr.read() };
// Ok(res)
// }
let result = super::impl_core::collect_into_array(&mut (0..N).map(|_| {
// See the documentation on `unclaim_bytes_read` as to why we're doing this here
decoder.unclaim_bytes_read(core::mem::size_of::<T>());
@ -499,7 +501,6 @@ where
// So this unwrap should never occur
result.unwrap()
}
}
}
impl Decode for () {

25
src/features/impl_alloc.rs
View File

@ -1,5 +1,5 @@
use crate::{
de::{read::Reader, BorrowDecoder, Decode, Decoder},
de::{BorrowDecoder, Decode, Decoder},
enc::{
self,
write::{SizeWriter, Writer},
@ -278,20 +278,23 @@ where
impl<T> Decode for Vec<T>
where
T: Decode + 'static,
T: Decode,
{
fn decode<D: Decoder>(decoder: &mut D) -> Result<Self, DecodeError> {
let len = crate::de::decode_slice_len(decoder)?;
if core::any::TypeId::of::<T>() == core::any::TypeId::of::<u8>() {
decoder.claim_container_read::<T>(len)?;
// optimize for reading u8 vecs
let mut vec = Vec::new();
vec.resize(len, 0u8);
decoder.reader().read(&mut vec)?;
// Safety: Vec<T> is Vec<u8>
return Ok(unsafe { core::mem::transmute(vec) });
}
// TODO: we can't limit `T: 'static` because that would break other things
// but we want to have this optimization
// This will be another contendor for specialization implementation
// if core::any::TypeId::of::<T>() == core::any::TypeId::of::<u8>() {
// decoder.claim_container_read::<T>(len)?;
// // optimize for reading u8 vecs
// let mut vec = Vec::new();
// vec.resize(len, 0u8);
// decoder.reader().read(&mut vec)?;
// // Safety: Vec<T> is Vec<u8>
// return Ok(unsafe { core::mem::transmute(vec) });
// }
decoder.claim_container_read::<T>(len)?;
let mut vec = Vec::with_capacity(len);

21
tests/std.rs
View File

@ -179,3 +179,24 @@ impl std::hash::Hasher for ExampleCustomHasher {
self.hash
}
}
#[test]
fn test_decode_borrow_str_in_array() {
let (strs, _): (Vec<&str>, usize) = bincode::borrow_decode_from_slice(
&[
3, 3, b'a', b'b', b'c', 3, b'd', b'e', b'f', 3, b'g', b'h', b'i',
],
bincode::config::standard(),
)
.unwrap();
assert_eq!(strs, vec!["abc", "def", "ghi"]);
let (strs, _): ([&str; 3], usize) = bincode::borrow_decode_from_slice(
&[
3, b'a', b'b', b'c', 3, b'd', b'e', b'f', 3, b'g', b'h', b'i',
],
bincode::config::standard(),
)
.unwrap();
assert_eq!(strs, ["abc", "def", "ghi"]);
}