Add method .into_inner()

src/lib.rs

@@ -323,6 +323,25 @@ impl<A: Array> ArrayVec<A> {
             }
         }
     }
+
+    /// Return the inner fixed size array, if it is full to its capacity.
+    ///
+    /// Return an **Ok** value with the array if length equals capacity,
+    /// return an **Err** with self otherwise.
+    ///
+    /// **Note:** This function may incur unproportionally large overhead
+    /// to move the array out, its performance is not optimal.
+    pub fn into_inner(self) -> Result<A, Self> {
+        if self.len() < self.capacity() {
+            Err(self)
+        } else {
+            unsafe {
+                let array = ptr::read(&*self.xs);
+                mem::forget(self);
+                Ok(array)
+            }
+        }
+    }
 }
 
 impl<A: Array> Deref for ArrayVec<A> {