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Auto merge of rust-lang#93572 - scottmcm:generic-iter-process, r=yaahc
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Change `ResultShunt` to be generic over `Try`

Just a refactor (and rename) for now, so it's not `Result`-specific.

This could be used for a future `Iterator::try_collect`, or similar, but anything like that is left for a future PR.
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bors committed Feb 8, 2022
2 parents 775e480 + 413945e commit 0c292c9
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Showing 6 changed files with 54 additions and 48 deletions.
78 changes: 38 additions & 40 deletions library/core/src/iter/adapters/mod.rs
Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
use crate::iter::{InPlaceIterable, Iterator};
use crate::ops::{ControlFlow, Try};
use crate::ops::{ChangeOutputType, ControlFlow, FromResidual, NeverShortCircuit, Residual, Try};

mod chain;
mod cloned;
Expand Down Expand Up @@ -128,59 +128,62 @@ pub unsafe trait SourceIter {
}

/// An iterator adapter that produces output as long as the underlying
/// iterator produces `Result::Ok` values.
/// iterator produces values where `Try::branch` says to `ControlFlow::Continue`.
///
/// If an error is encountered, the iterator stops and the error is
/// stored.
pub(crate) struct ResultShunt<'a, I, E> {
/// If a `ControlFlow::Break` is encountered, the iterator stops and the
/// residual is stored.
pub(crate) struct GenericShunt<'a, I, R> {
iter: I,
error: &'a mut Result<(), E>,
residual: &'a mut Option<R>,
}

/// Process the given iterator as if it yielded a `T` instead of a
/// `Result<T, _>`. Any errors will stop the inner iterator and
/// the overall result will be an error.
pub(crate) fn process_results<I, T, E, F, U>(iter: I, mut f: F) -> Result<U, E>
/// Process the given iterator as if it yielded a the item's `Try::Output`
/// type instead. Any `Try::Residual`s encountered will stop the inner iterator
/// and be propagated back to the overall result.
pub(crate) fn try_process<I, T, R, F, U>(iter: I, mut f: F) -> ChangeOutputType<I::Item, U>
where
I: Iterator<Item = Result<T, E>>,
for<'a> F: FnMut(ResultShunt<'a, I, E>) -> U,
I: Iterator<Item: Try<Output = T, Residual = R>>,
for<'a> F: FnMut(GenericShunt<'a, I, R>) -> U,
R: Residual<U>,
{
let mut error = Ok(());
let shunt = ResultShunt { iter, error: &mut error };
let mut residual = None;
let shunt = GenericShunt { iter, residual: &mut residual };
let value = f(shunt);
error.map(|()| value)
match residual {
Some(r) => FromResidual::from_residual(r),
None => Try::from_output(value),
}
}

impl<I, T, E> Iterator for ResultShunt<'_, I, E>
impl<I, R> Iterator for GenericShunt<'_, I, R>
where
I: Iterator<Item = Result<T, E>>,
I: Iterator<Item: Try<Residual = R>>,
{
type Item = T;
type Item = <I::Item as Try>::Output;

fn next(&mut self) -> Option<Self::Item> {
self.find(|_| true)
self.try_for_each(ControlFlow::Break).break_value()
}

fn size_hint(&self) -> (usize, Option<usize>) {
if self.error.is_err() {
if self.residual.is_some() {
(0, Some(0))
} else {
let (_, upper) = self.iter.size_hint();
(0, upper)
}
}

fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R
fn try_fold<B, F, T>(&mut self, init: B, mut f: F) -> T
where
F: FnMut(B, Self::Item) -> R,
R: Try<Output = B>,
F: FnMut(B, Self::Item) -> T,
T: Try<Output = B>,
{
let error = &mut *self.error;
self.iter
.try_fold(init, |acc, x| match x {
Ok(x) => ControlFlow::from_try(f(acc, x)),
Err(e) => {
*error = Err(e);
.try_fold(init, |acc, x| match Try::branch(x) {
ControlFlow::Continue(x) => ControlFlow::from_try(f(acc, x)),
ControlFlow::Break(r) => {
*self.residual = Some(r);
ControlFlow::Break(try { acc })
}
})
Expand All @@ -192,17 +195,12 @@ where
Self: Sized,
F: FnMut(B, Self::Item) -> B,
{
#[inline]
fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> {
move |acc, x| Ok(f(acc, x))
}

self.try_fold(init, ok(fold)).unwrap()
self.try_fold(init, NeverShortCircuit::wrap_mut_2(fold)).0
}
}

#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<I, E> SourceIter for ResultShunt<'_, I, E>
unsafe impl<I, R> SourceIter for GenericShunt<'_, I, R>
where
I: SourceIter,
{
Expand All @@ -215,11 +213,11 @@ where
}
}

// SAFETY: ResultShunt::next calls I::find, which has to advance `iter` in order to
// return `Some(_)`. Since `iter` has type `I: InPlaceIterable` it's guaranteed that
// at least one item will be moved out from the underlying source.
// SAFETY: GenericShunt::next calls `I::try_for_each`, which has to advance `iter`
// in order to return `Some(_)`. Since `iter` has type `I: InPlaceIterable` it's
// guaranteed that at least one item will be moved out from the underlying source.
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<I, T, E> InPlaceIterable for ResultShunt<'_, I, E> where
I: Iterator<Item = Result<T, E>> + InPlaceIterable
unsafe impl<I, T, R> InPlaceIterable for GenericShunt<'_, I, R> where
I: Iterator<Item: Try<Output = T, Residual = R>> + InPlaceIterable
{
}
2 changes: 1 addition & 1 deletion library/core/src/iter/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -417,7 +417,7 @@ pub use self::adapters::{
#[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")]
pub use self::adapters::{Intersperse, IntersperseWith};

pub(crate) use self::adapters::process_results;
pub(crate) use self::adapters::try_process;

mod adapters;
mod range;
Expand Down
8 changes: 4 additions & 4 deletions library/core/src/iter/traits/accum.rs
Original file line number Diff line number Diff line change
Expand Up @@ -167,7 +167,7 @@ where
where
I: Iterator<Item = Result<U, E>>,
{
iter::process_results(iter, |i| i.sum())
iter::try_process(iter, |i| i.sum())
}
}

Expand All @@ -183,7 +183,7 @@ where
where
I: Iterator<Item = Result<U, E>>,
{
iter::process_results(iter, |i| i.product())
iter::try_process(iter, |i| i.product())
}
}

Expand All @@ -210,7 +210,7 @@ where
where
I: Iterator<Item = Option<U>>,
{
iter.map(|x| x.ok_or(())).sum::<Result<_, _>>().ok()
iter::try_process(iter, |i| i.sum())
}
}

Expand All @@ -226,6 +226,6 @@ where
where
I: Iterator<Item = Option<U>>,
{
iter.map(|x| x.ok_or(())).product::<Result<_, _>>().ok()
iter::try_process(iter, |i| i.product())
}
}
8 changes: 8 additions & 0 deletions library/core/src/ops/try_trait.rs
Original file line number Diff line number Diff line change
Expand Up @@ -359,6 +359,14 @@ pub(crate) type ChangeOutputType<T, V> = <<T as Try>::Residual as Residual<V>>::
#[repr(transparent)]
pub(crate) struct NeverShortCircuit<T>(pub T);

impl<T> NeverShortCircuit<T> {
/// Wrap a binary `FnMut` to return its result wrapped in a `NeverShortCircuit`.
#[inline]
pub fn wrap_mut_2<A, B>(mut f: impl FnMut(A, B) -> T) -> impl FnMut(A, B) -> Self {
move |a, b| NeverShortCircuit(f(a, b))
}
}

pub(crate) enum NeverShortCircuitResidual {}

impl<T> Try for NeverShortCircuit<T> {
Expand Down
4 changes: 2 additions & 2 deletions library/core/src/option.rs
Original file line number Diff line number Diff line change
Expand Up @@ -500,7 +500,7 @@

#![stable(feature = "rust1", since = "1.0.0")]

use crate::iter::{FromIterator, FusedIterator, TrustedLen};
use crate::iter::{self, FromIterator, FusedIterator, TrustedLen};
use crate::panicking::{panic, panic_str};
use crate::pin::Pin;
use crate::{
Expand Down Expand Up @@ -2233,7 +2233,7 @@ impl<A, V: FromIterator<A>> FromIterator<Option<A>> for Option<V> {
// FIXME(#11084): This could be replaced with Iterator::scan when this
// performance bug is closed.

iter.into_iter().map(|x| x.ok_or(())).collect::<Result<_, _>>().ok()
iter::try_process(iter.into_iter(), |i| i.collect())
}
}

Expand Down
2 changes: 1 addition & 1 deletion library/core/src/result.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2016,7 +2016,7 @@ impl<A, E, V: FromIterator<A>> FromIterator<Result<A, E>> for Result<V, E> {
// FIXME(#11084): This could be replaced with Iterator::scan when this
// performance bug is closed.

iter::process_results(iter.into_iter(), |i| i.collect())
iter::try_process(iter.into_iter(), |i| i.collect())
}
}

Expand Down

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