Added impl Postings for Boxed and ref of postings.

src/postings/intersection.rs

@@ -109,4 +109,4 @@ pub fn intersection<'a>(postings: Vec<SegmentPostings<'a>>) -> IntersectionPosti
         })
         .collect();
     IntersectionPostings::new(boxed_postings)
-}
+}

src/postings/postings.rs

@@ -1,4 +1,6 @@
 use DocId;
+use std::borrow::Borrow;
+use std::borrow::BorrowMut;
 
 #[derive(PartialEq, Eq, Debug)]
 pub enum SkipResult {
@@ -12,13 +14,57 @@ pub trait Postings {
     // next needs to be called a first time to point to the correct element.
     fn next(&mut self,) -> bool;
     
-    fn doc(&self,) -> DocId;
-    
     // after skipping position
     // the iterator in such a way that doc() will return a
     // value greater or equal to target.
     fn skip_next(&mut self, target: DocId) -> SkipResult;
     
+    fn doc(&self,) -> DocId;
+
     fn doc_freq(&self,) -> usize;
 }
 
+impl<TPostings: Postings> Postings for Box<TPostings> {
+    fn next(&mut self,) -> bool {
+        let unboxed: &mut TPostings = self.borrow_mut();
+        unboxed.next()
+    }
+
+    fn skip_next(&mut self, target: DocId) -> SkipResult {
+        let unboxed: &mut TPostings = self.borrow_mut();
+        unboxed.skip_next(target)
+    }
+
+    fn doc(&self,) -> DocId {
+        let unboxed: &TPostings = self.borrow();
+        unboxed.borrow().doc()
+    }
+
+    fn doc_freq(&self,) -> usize {
+        let unboxed: &TPostings = self.borrow();
+        unboxed.doc_freq()
+    }
+}
+
+impl<'a, TPostings: Postings> Postings for &'a mut TPostings {
+    fn next(&mut self,) -> bool {
+        let unref: &mut TPostings = *self;
+        unref.next()
+    }
+        
+    fn skip_next(&mut self, target: DocId) -> SkipResult {
+        let unref: &mut TPostings = *self;
+        unref.skip_next(target)
+    }
+
+    fn doc(&self,) -> DocId {
+        let unref: &TPostings = *self;
+        unref.doc()
+    }
+
+    
+    fn doc_freq(&self,) -> usize {
+        let unref: &TPostings = *self;
+        unref.doc_freq()
+    }
+}