Expand .zip() specialization to .map() and .cloned()

src/libcore/iter/mod.rs

@@ -420,6 +420,18 @@ impl<'a, I, T: 'a> FusedIterator for Cloned<I>
     where I: FusedIterator<Item=&'a T>, T: Clone
 {}
 
+#[doc(hidden)]
+unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
+    where I: TrustedRandomAccess<Item=&'a T>, T: Clone
+{
+    unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
+        self.it.get_unchecked(i).clone()
+    }
+
+    #[inline]
+    fn may_have_side_effect() -> bool { true }
+}
+
 /// An iterator that repeats endlessly.
 ///
 /// This `struct` is created by the [`cycle()`] method on [`Iterator`]. See its
@@ -773,6 +785,13 @@ impl<A, B> ZipImpl<A, B> for Zip<A, B>
             unsafe {
                 Some((self.a.get_unchecked(i), self.b.get_unchecked(i)))
             }
+        } else if A::may_have_side_effect() && self.index < self.a.len() {
+            // match the base implementation's potential side effects
+            unsafe {
+                self.a.get_unchecked(self.index);
+            }
+            self.index += 1;
+            None
         } else {
             None
         }
@@ -789,6 +808,23 @@ impl<A, B> ZipImpl<A, B> for Zip<A, B>
         where A: DoubleEndedIterator + ExactSizeIterator,
               B: DoubleEndedIterator + ExactSizeIterator
     {
+        // Adjust a, b to equal length
+        if A::may_have_side_effect() {
+            let sz = self.a.len();
+            if sz > self.len {
+                for _ in 0..sz - cmp::max(self.len, self.index) {
+                    self.a.next_back();
+                }
+            }
+        }
+        if B::may_have_side_effect() {
+            let sz = self.b.len();
+            if sz > self.len {
+                for _ in 0..sz - self.len {
+                    self.b.next_back();
+                }
+            }
+        }
         if self.index < self.len {
             self.len -= 1;
             let i = self.len;
@@ -814,6 +850,9 @@ unsafe impl<A, B> TrustedRandomAccess for Zip<A, B>
         (self.a.get_unchecked(i), self.b.get_unchecked(i))
     }
 
+    fn may_have_side_effect() -> bool {
+        A::may_have_side_effect() || B::may_have_side_effect()
+    }
 }
 
 #[unstable(feature = "fused", issue = "35602")]
@@ -920,6 +959,18 @@ impl<B, I: ExactSizeIterator, F> ExactSizeIterator for Map<I, F>
 impl<B, I: FusedIterator, F> FusedIterator for Map<I, F>
     where F: FnMut(I::Item) -> B {}
 
+#[doc(hidden)]
+unsafe impl<B, I, F> TrustedRandomAccess for Map<I, F>
+    where I: TrustedRandomAccess,
+          F: FnMut(I::Item) -> B,
+{
+    unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
+        (self.f)(self.iter.get_unchecked(i))
+    }
+    #[inline]
+    fn may_have_side_effect() -> bool { true }
+}
+
 /// An iterator that filters the elements of `iter` with `predicate`.
 ///
 /// This `struct` is created by the [`filter()`] method on [`Iterator`]. See its
@@ -1135,6 +1186,10 @@ unsafe impl<I> TrustedRandomAccess for Enumerate<I>
     unsafe fn get_unchecked(&mut self, i: usize) -> (usize, I::Item) {
         (self.count + i, self.iter.get_unchecked(i))
     }
+
+    fn may_have_side_effect() -> bool {
+        I::may_have_side_effect()
+    }
 }
 
 #[unstable(feature = "fused", issue = "35602")]
@@ -1764,6 +1819,10 @@ unsafe impl<I> TrustedRandomAccess for Fuse<I>
     unsafe fn get_unchecked(&mut self, i: usize) -> I::Item {
         self.iter.get_unchecked(i)
     }
+
+    fn may_have_side_effect() -> bool {
+        I::may_have_side_effect()
+    }
 }
 
 #[unstable(feature = "fused", issue = "35602")]

src/libcore/iter_private.rs

@@ -14,12 +14,15 @@
 /// # Safety
 ///
 /// The iterator's .len() and size_hint() must be exact.
+/// `.len()` must be cheap to call.
 ///
 /// .get_unchecked() must return distinct mutable references for distinct
 /// indices (if applicable), and must return a valid reference if index is in
 /// 0..self.len().
 #[doc(hidden)]
 pub unsafe trait TrustedRandomAccess : ExactSizeIterator {
     unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item;
+    /// Return `true` if getting an iterator element may have
+    /// side effects. Remember to take inner iterators into account.
+    fn may_have_side_effect() -> bool;
 }
-

src/libcore/slice.rs

@@ -1968,11 +1968,13 @@ unsafe impl<'a, T> TrustedRandomAccess for Iter<'a, T> {
     unsafe fn get_unchecked(&mut self, i: usize) -> &'a T {
         &*self.ptr.offset(i as isize)
     }
+    fn may_have_side_effect() -> bool { false }
 }
 
 #[doc(hidden)]
 unsafe impl<'a, T> TrustedRandomAccess for IterMut<'a, T> {
     unsafe fn get_unchecked(&mut self, i: usize) -> &'a mut T {
         &mut *self.ptr.offset(i as isize)
     }
+    fn may_have_side_effect() -> bool { false }
 }

src/test/codegen/zip.rs

@@ -20,3 +20,12 @@ pub fn zip_copy(xs: &[u8], ys: &mut [u8]) {
         *y = *x;
     }
 }
+
+// CHECK-LABEL: @zip_copy_mapped
+#[no_mangle]
+pub fn zip_copy_mapped(xs: &[u8], ys: &mut [u8]) {
+// CHECK: memcpy
+    for (x, y) in xs.iter().map(|&x| x).zip(ys) {
+        *y = x;
+    }
+}

src/test/run-pass/iter-zip.rs

@@ -0,0 +1,112 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// 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.
+
+// Test that .zip() specialization preserves side effects
+// in sideeffectful iterator adaptors.
+
+use std::cell::Cell;
+
+#[derive(Debug)]
+struct CountClone(Cell<i32>);
+
+fn count_clone() -> CountClone { CountClone(Cell::new(0)) }
+
+impl PartialEq<i32> for CountClone {
+    fn eq(&self, rhs: &i32) -> bool {
+        self.0.get() == *rhs
+    }
+}
+
+impl Clone for CountClone {
+    fn clone(&self) -> Self {
+        let ret = CountClone(self.0.clone());
+        let n = self.0.get();
+        self.0.set(n + 1);
+        ret
+    }
+}
+
+fn test_zip_cloned_sideffectful() {
+    let xs = [count_clone(), count_clone(), count_clone(), count_clone()];
+    let ys = [count_clone(), count_clone()];
+
+    for _ in xs.iter().cloned().zip(ys.iter().cloned()) { }
+
+    assert_eq!(&xs, &[1, 1, 1, 0][..]);
+    assert_eq!(&ys, &[1, 1][..]);
+
+    let xs = [count_clone(), count_clone()];
+    let ys = [count_clone(), count_clone(), count_clone(), count_clone()];
+
+    for _ in xs.iter().cloned().zip(ys.iter().cloned()) { }
+
+    assert_eq!(&xs, &[1, 1][..]);
+    assert_eq!(&ys, &[1, 1, 0, 0][..]);
+}
+
+fn test_zip_map_sideffectful() {
+    let mut xs = [0; 6];
+    let mut ys = [0; 4];
+
+    for _ in xs.iter_mut().map(|x| *x += 1).zip(ys.iter_mut().map(|y| *y += 1)) { }
+
+    assert_eq!(&xs, &[1, 1, 1, 1, 1, 0]);
+    assert_eq!(&ys, &[1, 1, 1, 1]);
+
+    let mut xs = [0; 4];
+    let mut ys = [0; 6];
+
+    for _ in xs.iter_mut().map(|x| *x += 1).zip(ys.iter_mut().map(|y| *y += 1)) { }
+
+    assert_eq!(&xs, &[1, 1, 1, 1]);
+    assert_eq!(&ys, &[1, 1, 1, 1, 0, 0]);
+}
+
+fn test_zip_map_rev_sideffectful() {
+    let mut xs = [0; 6];
+    let mut ys = [0; 4];
+
+    {
+        let mut it = xs.iter_mut().map(|x| *x += 1).zip(ys.iter_mut().map(|y| *y += 1));
+        it.next_back();
+    }
+    assert_eq!(&xs, &[0, 0, 0, 1, 1, 1]);
+    assert_eq!(&ys, &[0, 0, 0, 1]);
+
+    let mut xs = [0; 6];
+    let mut ys = [0; 4];
+
+    {
+        let mut it = xs.iter_mut().map(|x| *x += 1).zip(ys.iter_mut().map(|y| *y += 1));
+        (&mut it).take(5).count();
+        it.next_back();
+    }
+    assert_eq!(&xs, &[1, 1, 1, 1, 1, 1]);
+    assert_eq!(&ys, &[1, 1, 1, 1]);
+}
+
+fn test_zip_nested_sideffectful() {
+    let mut xs = [0; 6];
+    let ys = [0; 4];
+
+    {
+        // test that it has the side effect nested inside enumerate
+        let it = xs.iter_mut().map(|x| *x = 1).enumerate().zip(&ys);
+        it.count();
+    }
+    assert_eq!(&xs, &[1, 1, 1, 1, 1, 0]);
+}
+
+fn main() {
+    test_zip_cloned_sideffectful();
+    test_zip_map_sideffectful();
+    test_zip_map_rev_sideffectful();
+    test_zip_nested_sideffectful();
+}