Auto merge of #48 - SergioBenitez:master, r=emilio

Add from_vec method for efficient creation from a Vec.

I also bumped the version to 0.3.3 for easy publishing.

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Author: bors-servo

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "smallvec"
-version = "0.3.2"
+version = "0.3.3"
 authors = ["Simon Sapin <simon.sapin@exyr.org>"]
 license = "MPL-2.0"
 repository = "https://github.com/servo/rust-smallvec"

lib.rs

@@ -207,6 +207,31 @@ impl<A: Array> SmallVec<A> {
         }
     }
 
+    /// Construct a new `SmallVec` from a `Vec<A::Item>` without copying
+    /// elements.
+    ///
+    /// ```rust
+    /// use smallvec::SmallVec;
+    ///
+    /// let vec = vec![1, 2, 3, 4, 5];
+    /// let small_vec: SmallVec<[_; 3]> = SmallVec::from_vec(vec);
+    ///
+    /// assert_eq!(&*small_vec, &[1, 2, 3, 4, 5]);
+    /// ```
+    #[inline]
+    pub fn from_vec(mut vec: Vec<A::Item>) -> SmallVec<A> {
+        let (ptr, cap, len) = (vec.as_mut_ptr(), vec.capacity(), vec.len());
+        mem::forget(vec);
+
+        SmallVec {
+            len: len,
+            data: SmallVecData::Heap {
+                ptr: ptr,
+                capacity: cap
+            }
+        }
+    }
+
     /// Sets the length of a vector.
     ///
     /// This will explicitly set the size of the vector, without actually
@@ -1363,4 +1388,37 @@ pub mod tests {
         let vec = SmallVec::<[u8; 2]>::from_iter(0..3);
         assert_eq!(vec.into_vec(), vec![0, 1, 2]);
     }
+
+    #[test]
+    fn test_from_vec() {
+        let vec = vec![];
+        let small_vec: SmallVec<[u8; 3]> = SmallVec::from_vec(vec);
+        assert_eq!(&*small_vec, &[]);
+        drop(small_vec);
+
+        let vec = vec![];
+        let small_vec: SmallVec<[u8; 1]> = SmallVec::from_vec(vec);
+        assert_eq!(&*small_vec, &[]);
+        drop(small_vec);
+
+        let vec = vec![1];
+        let small_vec: SmallVec<[u8; 3]> = SmallVec::from_vec(vec);
+        assert_eq!(&*small_vec, &[1]);
+        drop(small_vec);
+
+        let vec = vec![1, 2, 3];
+        let small_vec: SmallVec<[u8; 3]> = SmallVec::from_vec(vec);
+        assert_eq!(&*small_vec, &[1, 2, 3]);
+        drop(small_vec);
+
+        let vec = vec![1, 2, 3, 4, 5];
+        let small_vec: SmallVec<[u8; 3]> = SmallVec::from_vec(vec);
+        assert_eq!(&*small_vec, &[1, 2, 3, 4, 5]);
+        drop(small_vec);
+
+        let vec = vec![1, 2, 3, 4, 5];
+        let small_vec: SmallVec<[u8; 1]> = SmallVec::from_vec(vec);
+        assert_eq!(&*small_vec, &[1, 2, 3, 4, 5]);
+        drop(small_vec);
+    }
 }