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refactor: moving DrainFilter into drain_filter.rs

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C 2020-12-04 23:58:11 +00:00
parent 5182776c6c
commit 434e5d1422
2 changed files with 148 additions and 138 deletions
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143
library/alloc/src/vec/drain_filter.rs Normal file
View file

@ -0,0 +1,143 @@
use core::ptr::{self};
use core::slice::{self};
use crate::alloc::{Allocator, Global};
use super::{Vec};
/// An iterator which uses a closure to determine if an element should be removed.
///
/// This struct is created by [`Vec::drain_filter`].
/// See its documentation for more.
///
/// # Example
///
/// ```
/// #![feature(drain_filter)]
///
/// let mut v = vec![0, 1, 2];
/// let iter: std::vec::DrainFilter<_, _> = v.drain_filter(|x| *x % 2 == 0);
/// ```
#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
#[derive(Debug)]
pub struct DrainFilter<
'a,
T,
F,
#[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
> where
F: FnMut(&mut T) -> bool,
{
pub(super) vec: &'a mut Vec<T, A>,
/// The index of the item that will be inspected by the next call to `next`.
pub(super) idx: usize,
/// The number of items that have been drained (removed) thus far.
pub(super) del: usize,
/// The original length of `vec` prior to draining.
pub(super) old_len: usize,
/// The filter test predicate.
pub(super) pred: F,
/// A flag that indicates a panic has occurred in the filter test predicate.
/// This is used as a hint in the drop implementation to prevent consumption
/// of the remainder of the `DrainFilter`. Any unprocessed items will be
/// backshifted in the `vec`, but no further items will be dropped or
/// tested by the filter predicate.
pub(super) panic_flag: bool,
}
impl<T, F, A: Allocator> DrainFilter<'_, T, F, A>
where
F: FnMut(&mut T) -> bool,
{
/// Returns a reference to the underlying allocator.
#[unstable(feature = "allocator_api", issue = "32838")]
#[inline]
pub fn allocator(&self) -> &A {
self.vec.allocator()
}
}
#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
impl<T, F, A: Allocator> Iterator for DrainFilter<'_, T, F, A>
where
F: FnMut(&mut T) -> bool,
{
type Item = T;
fn next(&mut self) -> Option<T> {
unsafe {
while self.idx < self.old_len {
let i = self.idx;
let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
self.panic_flag = true;
let drained = (self.pred)(&mut v[i]);
self.panic_flag = false;
// Update the index *after* the predicate is called. If the index
// is updated prior and the predicate panics, the element at this
// index would be leaked.
self.idx += 1;
if drained {
self.del += 1;
return Some(ptr::read(&v[i]));
} else if self.del > 0 {
let del = self.del;
let src: *const T = &v[i];
let dst: *mut T = &mut v[i - del];
ptr::copy_nonoverlapping(src, dst, 1);
}
}
None
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
(0, Some(self.old_len - self.idx))
}
}
#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
impl<T, F, A: Allocator> Drop for DrainFilter<'_, T, F, A>
where
F: FnMut(&mut T) -> bool,
{
fn drop(&mut self) {
struct BackshiftOnDrop<'a, 'b, T, F, A: Allocator>
where
F: FnMut(&mut T) -> bool,
{
drain: &'b mut DrainFilter<'a, T, F, A>,
}
impl<'a, 'b, T, F, A: Allocator> Drop for BackshiftOnDrop<'a, 'b, T, F, A>
where
F: FnMut(&mut T) -> bool,
{
fn drop(&mut self) {
unsafe {
if self.drain.idx < self.drain.old_len && self.drain.del > 0 {
// This is a pretty messed up state, and there isn't really an
// obviously right thing to do. We don't want to keep trying
// to execute `pred`, so we just backshift all the unprocessed
// elements and tell the vec that they still exist. The backshift
// is required to prevent a double-drop of the last successfully
// drained item prior to a panic in the predicate.
let ptr = self.drain.vec.as_mut_ptr();
let src = ptr.add(self.drain.idx);
let dst = src.sub(self.drain.del);
let tail_len = self.drain.old_len - self.drain.idx;
src.copy_to(dst, tail_len);
}
self.drain.vec.set_len(self.drain.old_len - self.drain.del);
}
}
}
let backshift = BackshiftOnDrop { drain: self };
// Attempt to consume any remaining elements if the filter predicate
// has not yet panicked. We'll backshift any remaining elements
// whether we've already panicked or if the consumption here panics.
if !backshift.drain.panic_flag {
backshift.drain.for_each(drop);
}
}
}

143
library/alloc/src/vec/mod.rs
View file

@ -74,6 +74,11 @@ use crate::boxed::Box;
use crate::collections::TryReserveError; use crate::collections::TryReserveError;
use crate::raw_vec::RawVec; use crate::raw_vec::RawVec;
#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
pub use self::drain_filter::DrainFilter;
mod drain_filter;
/// A contiguous growable array type, written `Vec<T>` but pronounced 'vector'. /// A contiguous growable array type, written `Vec<T>` but pronounced 'vector'.
/// ///
/// # Examples /// # Examples
@ -3585,141 +3590,3 @@ impl<T, A: Allocator> Drain<'_, T, A> {
self.tail_start = new_tail_start; self.tail_start = new_tail_start;
} }
} }
/// An iterator which uses a closure to determine if an element should be removed.
///
/// This struct is created by [`Vec::drain_filter`].
/// See its documentation for more.
///
/// # Example
///
/// ```
/// #![feature(drain_filter)]
///
/// let mut v = vec![0, 1, 2];
/// let iter: std::vec::DrainFilter<_, _> = v.drain_filter(|x| *x % 2 == 0);
/// ```
#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
#[derive(Debug)]
pub struct DrainFilter<
'a,
T,
F,
#[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
> where
F: FnMut(&mut T) -> bool,
{
vec: &'a mut Vec<T, A>,
/// The index of the item that will be inspected by the next call to `next`.
idx: usize,
/// The number of items that have been drained (removed) thus far.
del: usize,
/// The original length of `vec` prior to draining.
old_len: usize,
/// The filter test predicate.
pred: F,
/// A flag that indicates a panic has occurred in the filter test predicate.
/// This is used as a hint in the drop implementation to prevent consumption
/// of the remainder of the `DrainFilter`. Any unprocessed items will be
/// backshifted in the `vec`, but no further items will be dropped or
/// tested by the filter predicate.
panic_flag: bool,
}
impl<T, F, A: Allocator> DrainFilter<'_, T, F, A>
where
F: FnMut(&mut T) -> bool,
{
/// Returns a reference to the underlying allocator.
#[unstable(feature = "allocator_api", issue = "32838")]
#[inline]
pub fn allocator(&self) -> &A {
self.vec.allocator()
}
}
#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
impl<T, F, A: Allocator> Iterator for DrainFilter<'_, T, F, A>
where
F: FnMut(&mut T) -> bool,
{
type Item = T;
fn next(&mut self) -> Option<T> {
unsafe {
while self.idx < self.old_len {
let i = self.idx;
let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
self.panic_flag = true;
let drained = (self.pred)(&mut v[i]);
self.panic_flag = false;
// Update the index *after* the predicate is called. If the index
// is updated prior and the predicate panics, the element at this
// index would be leaked.
self.idx += 1;
if drained {
self.del += 1;
return Some(ptr::read(&v[i]));
} else if self.del > 0 {
let del = self.del;
let src: *const T = &v[i];
let dst: *mut T = &mut v[i - del];
ptr::copy_nonoverlapping(src, dst, 1);
}
}
None
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
(0, Some(self.old_len - self.idx))
}
}
#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
impl<T, F, A: Allocator> Drop for DrainFilter<'_, T, F, A>
where
F: FnMut(&mut T) -> bool,
{
fn drop(&mut self) {
struct BackshiftOnDrop<'a, 'b, T, F, A: Allocator>
where
F: FnMut(&mut T) -> bool,
{
drain: &'b mut DrainFilter<'a, T, F, A>,
}
impl<'a, 'b, T, F, A: Allocator> Drop for BackshiftOnDrop<'a, 'b, T, F, A>
where
F: FnMut(&mut T) -> bool,
{
fn drop(&mut self) {
unsafe {
if self.drain.idx < self.drain.old_len && self.drain.del > 0 {
// This is a pretty messed up state, and there isn't really an
// obviously right thing to do. We don't want to keep trying
// to execute `pred`, so we just backshift all the unprocessed
// elements and tell the vec that they still exist. The backshift
// is required to prevent a double-drop of the last successfully
// drained item prior to a panic in the predicate.
let ptr = self.drain.vec.as_mut_ptr();
let src = ptr.add(self.drain.idx);
let dst = src.sub(self.drain.del);
let tail_len = self.drain.old_len - self.drain.idx;
src.copy_to(dst, tail_len);
}
self.drain.vec.set_len(self.drain.old_len - self.drain.del);
}
}
}
let backshift = BackshiftOnDrop { drain: self };
// Attempt to consume any remaining elements if the filter predicate
// has not yet panicked. We'll backshift any remaining elements
// whether we've already panicked or if the consumption here panics.
if !backshift.drain.panic_flag {
backshift.drain.for_each(drop);
}
}
}