From c6e027207c64bd6da431982a12217c29556d32bd Mon Sep 17 00:00:00 2001
From: Jakob Stoklund Olesen <jolesen@mozilla.com>
Date: Thu, 6 Apr 2017 13:58:48 -0700
Subject: [PATCH] Add an iterators module with extra Iterator methods.

Start with an adjacent_pairs() iterator adapter.
---
 lib/cretonne/src/iterators.rs | 90 +++++++++++++++++++++++++++++++++++
 lib/cretonne/src/lib.rs       |  3 +-
 2 files changed, 92 insertions(+), 1 deletion(-)
 create mode 100644 lib/cretonne/src/iterators.rs

diff --git a/lib/cretonne/src/iterators.rs b/lib/cretonne/src/iterators.rs
new file mode 100644
index 0000000000..3bdc3cc1cb
--- /dev/null
+++ b/lib/cretonne/src/iterators.rs
@@ -0,0 +1,90 @@
+//! Iterator utilities.
+
+/// Extra methods for iterators.
+pub trait IteratorExtras: Iterator {
+    /// Create an iterator that produces adjacent pairs of elements from the iterator.
+    fn adjacent_pairs(mut self) -> AdjacentPairs<Self>
+        where Self: Sized,
+              Self::Item: Clone
+    {
+        let elem = self.next();
+        AdjacentPairs {
+            iter: self,
+            elem: elem,
+        }
+    }
+}
+
+impl<T> IteratorExtras for T where T: Iterator {}
+
+/// Adjacent pairs iterator returned by `adjacent_pairs()`.
+///
+/// This wraps another iterator and produces a sequence of adjacent pairs of elements.
+pub struct AdjacentPairs<I>
+    where I: Iterator,
+          I::Item: Clone
+{
+    iter: I,
+    elem: Option<I::Item>,
+}
+
+impl<I> Iterator for AdjacentPairs<I>
+    where I: Iterator,
+          I::Item: Clone
+{
+    type Item = (I::Item, I::Item);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.elem
+            .take()
+            .and_then(|e| {
+                          self.elem = self.iter.next();
+                          self.elem.clone().map(|n| (e, n))
+                      })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn adjpairs() {
+        use super::IteratorExtras;
+
+        assert_eq!([1, 2, 3, 4]
+                       .iter()
+                       .cloned()
+                       .adjacent_pairs()
+                       .collect::<Vec<_>>(),
+                   vec![(1, 2), (2, 3), (3, 4)]);
+        assert_eq!([2, 3, 4]
+                       .iter()
+                       .cloned()
+                       .adjacent_pairs()
+                       .collect::<Vec<_>>(),
+                   vec![(2, 3), (3, 4)]);
+        assert_eq!([2, 3, 4]
+                       .iter()
+                       .cloned()
+                       .adjacent_pairs()
+                       .collect::<Vec<_>>(),
+                   vec![(2, 3), (3, 4)]);
+        assert_eq!([3, 4]
+                       .iter()
+                       .cloned()
+                       .adjacent_pairs()
+                       .collect::<Vec<_>>(),
+                   vec![(3, 4)]);
+        assert_eq!([4]
+                       .iter()
+                       .cloned()
+                       .adjacent_pairs()
+                       .collect::<Vec<_>>(),
+                   vec![]);
+        assert_eq!([]
+                       .iter()
+                       .cloned()
+                       .adjacent_pairs()
+                       .collect::<Vec<(i32, i32)>>(),
+                   vec![]);
+    }
+}
diff --git a/lib/cretonne/src/lib.rs b/lib/cretonne/src/lib.rs
index 1c983c74e6..e44899f8c2 100644
--- a/lib/cretonne/src/lib.rs
+++ b/lib/cretonne/src/lib.rs
@@ -14,10 +14,10 @@ pub const VERSION: &'static str = env!("CARGO_PKG_VERSION");
 pub mod dbg;
 
 pub mod binemit;
-pub mod flowgraph;
 pub mod dominator_tree;
 pub mod entity_list;
 pub mod entity_map;
+pub mod flowgraph;
 pub mod ir;
 pub mod isa;
 pub mod regalloc;
@@ -28,6 +28,7 @@ pub mod verifier;
 mod abi;
 mod constant_hash;
 mod context;
+mod iterators;
 mod legalizer;
 mod packed_option;
 mod partition_slice;