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Remove data structure specialization for .zip() iterator #36490

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Sep 17, 2016
Merged

Remove data structure specialization for .zip() iterator #36490

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52 changes: 14 additions & 38 deletions src/libcore/iter/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -643,7 +643,9 @@ impl<A, B> FusedIterator for Chain<A, B>
pub struct Zip<A, B> {
a: A,
b: B,
spec: <(A, B) as ZipImplData>::Data,
// index and len are only used by the specialized version of zip
index: usize,
len: usize,
}

#[stable(feature = "rust1", since = "1.0.0")]
Expand Down Expand Up @@ -685,17 +687,6 @@ trait ZipImpl<A, B> {
B: DoubleEndedIterator + ExactSizeIterator;
}

// Zip specialization data members
#[doc(hidden)]
trait ZipImplData {
type Data: 'static + Clone + Default + fmt::Debug;
}

#[doc(hidden)]
impl<T> ZipImplData for T {
default type Data = ();
}

// General Zip impl
#[doc(hidden)]
impl<A, B> ZipImpl<A, B> for Zip<A, B>
Expand All @@ -706,7 +697,8 @@ impl<A, B> ZipImpl<A, B> for Zip<A, B>
Zip {
a: a,
b: b,
spec: Default::default(), // unused
index: 0, // unused
len: 0, // unused
}
}

Expand Down Expand Up @@ -759,20 +751,6 @@ impl<A, B> ZipImpl<A, B> for Zip<A, B>
}
}

#[doc(hidden)]
#[derive(Default, Debug, Clone)]
struct ZipImplFields {
index: usize,
len: usize,
}

#[doc(hidden)]
impl<A, B> ZipImplData for (A, B)
where A: TrustedRandomAccess, B: TrustedRandomAccess
{
type Data = ZipImplFields;
}

#[doc(hidden)]
impl<A, B> ZipImpl<A, B> for Zip<A, B>
where A: TrustedRandomAccess, B: TrustedRandomAccess
Expand All @@ -782,18 +760,16 @@ impl<A, B> ZipImpl<A, B> for Zip<A, B>
Zip {
a: a,
b: b,
spec: ZipImplFields {
index: 0,
len: len,
}
index: 0,
len: len,
}
}

#[inline]
fn next(&mut self) -> Option<(A::Item, B::Item)> {
if self.spec.index < self.spec.len {
let i = self.spec.index;
self.spec.index += 1;
if self.index < self.len {
let i = self.index;
self.index += 1;
unsafe {
Some((self.a.get_unchecked(i), self.b.get_unchecked(i)))
}
Expand All @@ -804,7 +780,7 @@ impl<A, B> ZipImpl<A, B> for Zip<A, B>

#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let len = self.spec.len - self.spec.index;
let len = self.len - self.index;
(len, Some(len))
}

Expand All @@ -813,9 +789,9 @@ impl<A, B> ZipImpl<A, B> for Zip<A, B>
where A: DoubleEndedIterator + ExactSizeIterator,
B: DoubleEndedIterator + ExactSizeIterator
{
if self.spec.index < self.spec.len {
self.spec.len -= 1;
let i = self.spec.len;
if self.index < self.len {
self.len -= 1;
let i = self.len;
unsafe {
Some((self.a.get_unchecked(i), self.b.get_unchecked(i)))
}
Expand Down
17 changes: 17 additions & 0 deletions src/test/run-pass/variance-iterators-in-libcore.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,17 @@
// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
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@nagisa nagisa Sep 15, 2016 •
edited
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NIT: Name for this test is weirdly general for what it tests. Linked list iterator covariance is tested in libcollections itself for example. Perhaps we could test for zip covariance in libcoretest too?

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It's a place to put more iterator tests, for now just this one.

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@bluss my experience suggests that people rarely reuse/update tests and instead just add new ones. The only exception I can think of is when some area belongs to one person and they do all the work in it.

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I think it has happened before in the various run-pass/sync-send-*.rs files

// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

#![allow(warnings)]

use std::iter::Zip;

fn zip_covariant<'a, A, B>(iter: Zip<&'static A, &'static B>) -> Zip<&'a A, &'a B> { iter }

fn main() { }