Define virtual destructor for IndexScorer

It must be defined in order for any `std::unique_ptr<IndexScorer>` to
execute the correct deleter when it goes out of scope. Because we define
the constructor, we also define the copy/move constructor/operator, and
in turn also default constructor, which we need.

Signed-off-by: Michal Siedlaczek <[email protected]>

include/pisa/scorer/index_scorer.hpp

@@ -10,12 +10,18 @@ using TermScorer = std::function<float(uint32_t, uint32_t)>;
 /** Index scorer construct scorers for terms in the index. */
 class IndexScorer {
   public:
+    IndexScorer() = default;
+    IndexScorer(const IndexScorer&) = default;
+    IndexScorer(IndexScorer&&) noexcept = default;
+    IndexScorer& operator=(const IndexScorer&) = delete;
+    IndexScorer& operator=(IndexScorer&&) noexcept = delete;
+    virtual ~IndexScorer() = default;
     virtual TermScorer term_scorer(std::uint64_t term_id) const = 0;
 };
 
 /** Index scorer using WAND metadata for scoring. */
 template <typename Wand>
-struct WandIndexScorer: IndexScorer {
+struct WandIndexScorer: public IndexScorer {
   protected:
     const Wand& m_wdata;