Add Itertools::copied

src/adaptors/mod.rs

@@ -24,6 +24,52 @@ macro_rules! clone_fields {
         }
     );
 }
+/// An iterator that copies the elements of an underlying iterator.
+///
+/// See [`.copied()`](../trait.Itertools.html#method.copied) for more information.
+#[derive(Clone, Debug)]
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+pub struct Copied<I> {
+    it: I
+}
+
+pub fn copied<'a, I, T>(iterable: I) -> Copied<I::IntoIter>
+    where I: IntoIterator<Item=&'a T>,
+          T: 'a + Copy
+{
+    Copied { it: iterable.into_iter() }
+}
+
+impl<'a, I, T> Iterator for Copied<I>
+    where I: Iterator<Item=&'a T>,
+          T: Copy + 'a
+{
+    type Item = T;
+    #[inline]
+    fn next(&mut self) -> Option<T> {
+        self.it.next().map(|&x| x)
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.it.size_hint()
+    }
+}
+
+impl<'a, I, T> ExactSizeIterator for Copied<I>
+    where I: ExactSizeIterator<Item=&'a T>,
+          T: Copy + 'a
+{}
+
+impl<'a, I, T> DoubleEndedIterator for Copied<I>
+    where I: DoubleEndedIterator<Item=&'a T>,
+          T: Copy + 'a
+{
+    #[inline]
+    fn next_back(&mut self) -> Option<T> {
+        self.it.next_back().map(|&x| x)
+    }
+}
 
 /// An iterator adaptor that alternates elements from two iterators until both
 /// run out.

src/lib.rs

@@ -51,6 +51,7 @@ pub use std::iter as __std_iter;
 /// The concrete iterator types.
 pub mod structs {
     pub use adaptors::{
+        Copied,
         Dedup,
         Interleave,
         InterleaveShortest,
@@ -1983,6 +1984,33 @@ pub trait Itertools : Iterator {
             |x, y, _, _| Ordering::Less == compare(x, y)
         )
     }
+
+    /// Creates an iterator which copies all of its elements.
+    ///
+    /// This is useful when you have an iterator over `&T`, but you need an
+    /// iterator over `T`. It works like `Iterator::cloned`, but requires
+    /// `T` to implement `Copy`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use itertools::Itertools;
+    ///
+    /// let a = [1, 2, 3];
+    ///
+    /// let v_copied: Vec<_> = a.iter().copied().collect();
+    ///
+    /// // copied is the same as .map(|&x| x)
+    /// let v_map: Vec<_> = a.iter().map(|&x| x).collect();
+    ///
+    /// assert_eq!(v_copied, vec![1, 2, 3]);
+    /// assert_eq!(v_map, vec![1, 2, 3]);
+    /// ```
+    fn copied<'a, T>(self) -> Copied<Self>
+        where Self: Sized + Iterator<Item=&'a T>, T: 'a + Copy
+    {
+        adaptors::copied(self)
+    }
 }
 
 impl<T: ?Sized> Itertools for T where T: Iterator { }

tests/test_core.rs

@@ -75,7 +75,7 @@ fn izip3() {
 fn write_to() {
     let xs = [7, 9, 8];
     let mut ys = [0; 5];
-    let cnt = ys.iter_mut().set_from(xs.iter().map(|x| *x));
+    let cnt = ys.iter_mut().set_from(xs.iter().copied());
     assert!(cnt == xs.len());
     assert!(ys == [7, 9, 8, 0, 0]);
 
@@ -238,3 +238,12 @@ fn tree_fold1() {
         assert_eq!((0..i).tree_fold1(|x, y| x + y), (0..i).fold1(|x, y| x + y));
     }
 }
+
+#[test]
+fn test_copied() {
+    let a = [1, 2, 3, 4, 5];
+    let mut copied = a.iter().copied();
+    assert_eq!(copied.next(), Some(1));
+    assert_eq!(copied.next_back(), Some(5));
+    it::assert_equal(copied, [2, 3, 4].iter().cloned());
+}