Downcast TermScorer for intersection when all legs are TermScorers

Cargo.toml

@@ -41,6 +41,7 @@ error-chain = "0.8"
 owning_ref = "0.3"
 stable_deref_trait = "1.0.0"
 rust-stemmers = "0.1.0"
+downcast = "0.9"
 
 [target.'cfg(windows)'.dependencies]
 winapi = "0.2"

src/lib.rs

@@ -167,6 +167,9 @@ extern crate test;
 
 extern crate tinysegmenter;
 
+#[macro_use]
+extern crate downcast;
+
 #[cfg(test)]
 mod functional_test;
 

src/query/boolean_query/boolean_weight.rs

@@ -4,6 +4,9 @@ use postings::{Intersection, Union};
 use std::collections::HashMap;
 use query::EmptyScorer;
 use query::Scorer;
+use downcast::Downcast;
+use query::term_query::TermScorer;
+use std::borrow::Borrow;
 use query::Exclude;
 use query::Occur;
 use query::RequiredOptionalScorer;
@@ -59,8 +62,26 @@ impl BooleanWeight {
                 if scorers.len() == 1 {
                     scorers.into_iter().next().unwrap()
                 } else {
-                    let scorer: Box<Scorer> = box Intersection::from(scorers);
-                    scorer
+                    if scorers
+                        .iter()
+                        .all(|scorer| {
+                            let scorer_ref:&Scorer = scorer.borrow();
+                            Downcast::<TermScorer>::is_type(scorer_ref)
+                        }) {
+                        let scorers: Vec<TermScorer> = scorers.into_iter()
+                            .map(|scorer| {
+                                *Downcast::<TermScorer>::downcast(scorer)
+                                    .expect("downcasting should not have failed, we\
+                                    checked in advance that the type were correct.")
+
+                            })
+                            .collect();
+                        let scorer: Box<Scorer> = box Intersection::from(scorers);
+                        scorer
+                    } else {
+                        let scorer: Box<Scorer> = box Intersection::from(scorers);
+                        scorer
+                    }
                 }
             });
 

src/query/scorer.rs

@@ -5,11 +5,12 @@ use collector::Collector;
 use postings::SkipResult;
 use common::BitSet;
 use std::ops::DerefMut;
+use downcast;
 
 /// Scored set of documents matching a query within a specific segment.
 ///
 /// See [`Query`](./trait.Query.html).
-pub trait Scorer: DocSet + 'static {
+pub trait Scorer: downcast::Any + DocSet + 'static {
     /// Returns the score.
     ///
     /// This method will perform a bit of computation and is not cached.
@@ -24,6 +25,8 @@ pub trait Scorer: DocSet + 'static {
     }
 }
 
+downcast!(Scorer);
+
 impl<'a> Scorer for Box<Scorer + 'a> {
     fn score(&mut self) -> Score {
         self.deref_mut().score()