Change implementation of syntax::util::SmallVector to use data_structures::SmallVec.

1 files changed, 49 insertions, 0 deletions

diff --git a/src/libsyntax/util/move_map.rs b/src/libsyntax/util/move_map.rs
index e1078b719bf..fe05e2958b3 100644
--- a/src/libsyntax/util/move_map.rs
+++ b/src/libsyntax/util/move_map.rs
@@ -10,6 +10,8 @@
 
 use std::ptr;
 
+use util::small_vector::SmallVector;
+
 pub trait MoveMap<T>: Sized {
     fn move_map<F>(self, mut f: F) -> Self where F: FnMut(T) -> T {
         self.move_flat_map(|e| Some(f(e)))
@@ -75,3 +77,50 @@ impl<T> MoveMap<T> for ::ptr::P<[T]> {
         ::ptr::P::from_vec(self.into_vec().move_flat_map(f))
     }
 }
+
+impl<T> MoveMap<T> for SmallVector<T> {
+    fn move_flat_map<F, I>(mut self, mut f: F) -> Self
+        where F: FnMut(T) -> I,
+              I: IntoIterator<Item=T>
+    {
+        let mut read_i = 0;
+        let mut write_i = 0;
+        unsafe {
+            let mut old_len = self.len();
+            self.set_len(0); // make sure we just leak elements in case of panic
+
+            while read_i < old_len {
+                // move the read_i'th item out of the vector and map it
+                // to an iterator
+                let e = ptr::read(self.get_unchecked(read_i));
+                let mut iter = f(e).into_iter();
+                read_i += 1;
+
+                while let Some(e) = iter.next() {
+                    if write_i < read_i {
+                        ptr::write(self.get_unchecked_mut(write_i), e);
+                        write_i += 1;
+                    } else {
+                        // If this is reached we ran out of space
+                        // in the middle of the vector.
+                        // However, the vector is in a valid state here,
+                        // so we just do a somewhat inefficient insert.
+                        self.set_len(old_len);
+                        self.insert(write_i, e);
+
+                        old_len = self.len();
+                        self.set_len(0);
+
+                        read_i += 1;
+                        write_i += 1;
+                    }
+                }
+            }
+
+            // write_i tracks the number of actually written new items.
+            self.set_len(write_i);
+        }
+
+        self
+    }
+}