chore: add empty constructor for Ruby GC

Author: yoshoku

ext/hnswlib/src/bruteforce.h

@@ -21,6 +21,7 @@ class BruteforceSearch : public AlgorithmInterface<dist_t> {
 
     std::unordered_map<labeltype, size_t > dict_external_to_internal;
 
+    BruteforceSearch() : data_(nullptr) { }
 
     BruteforceSearch(SpaceInterface <dist_t> *s)
         : data_(nullptr),

ext/hnswlib/src/hnswalg.h

@@ -70,6 +70,7 @@ class HierarchicalNSW : public AlgorithmInterface<dist_t> {
     std::mutex deleted_elements_lock;  // lock for deleted_elements
     std::unordered_set<tableint> deleted_elements;  // contains internal ids of deleted elements
 
+    HierarchicalNSW() { }
 
     HierarchicalNSW(SpaceInterface<dist_t> *s) {
     }
@@ -322,7 +323,7 @@ class HierarchicalNSW : public AlgorithmInterface<dist_t> {
         std::priority_queue<std::pair<dist_t, tableint>, std::vector<std::pair<dist_t, tableint>>, CompareByFirst> candidate_set;
 
         dist_t lowerBound;
-        if (bare_bone_search || 
+        if (bare_bone_search ||
             (!isMarkedDeleted(ep_id) && ((!isIdAllowed) || (*isIdAllowed)(getExternalLabel(ep_id))))) {
             char* ep_data = getDataByInternalId(ep_id);
             dist_t dist = fstdistfunc_(data_point, ep_data, dist_func_param_);
@@ -403,7 +404,7 @@ class HierarchicalNSW : public AlgorithmInterface<dist_t> {
                                         _MM_HINT_T0);  ////////////////////////
 #endif
 
-                        if (bare_bone_search || 
+                        if (bare_bone_search ||
                             (!isMarkedDeleted(candidate_id) && ((!isIdAllowed) || (*isIdAllowed)(getExternalLabel(candidate_id))))) {
                             top_candidates.emplace(dist, candidate_id);
                             if (!bare_bone_search && stop_condition) {
@@ -826,7 +827,7 @@ class HierarchicalNSW : public AlgorithmInterface<dist_t> {
     std::vector<data_t> getDataByLabel(labeltype label) const {
         // lock all operations with element by label
         std::unique_lock <std::mutex> lock_label(getLabelOpMutex(label));
-        
+
         std::unique_lock <std::mutex> lock_table(label_lookup_lock);
         auto search = label_lookup_.find(label);
         if (search == label_lookup_.end() || isMarkedDeleted(search->second)) {
@@ -888,7 +889,7 @@ class HierarchicalNSW : public AlgorithmInterface<dist_t> {
 
     /*
     * Removes the deleted mark of the node, does NOT really change the current graph.
-    * 
+    *
     * Note: the method is not safe to use when replacement of deleted elements is enabled,
     *  because elements marked as deleted can be completely removed by addPoint
     */

ext/hnswlib/src/space_ip.h

@@ -158,7 +158,7 @@ InnerProductSIMD16ExtAVX512(const void *pVect1v, const void *pVect2v, const void
     __m512 sum512 = _mm512_set1_ps(0);
 
     size_t loop = qty16 / 4;
-    
+
     while (loop--) {
         __m512 v1 = _mm512_loadu_ps(pVect1);
         __m512 v2 = _mm512_loadu_ps(pVect2);
@@ -345,6 +345,8 @@ class InnerProductSpace : public SpaceInterface<float> {
     size_t dim_;
 
  public:
+    InnerProductSpace() : data_size_(0), dim_(0) { }
+
     InnerProductSpace(size_t dim) {
         fstdistfunc_ = InnerProductDistance;
 #if defined(USE_AVX) || defined(USE_SSE) || defined(USE_AVX512)

ext/hnswlib/src/space_l2.h

@@ -211,6 +211,8 @@ class L2Space : public SpaceInterface<float> {
     size_t dim_;
 
  public:
+    L2Space() : data_size_(0), dim_(0) { }
+
     L2Space(size_t dim) {
         fstdistfunc_ = L2Sqr;
 #if defined(USE_SSE) || defined(USE_AVX) || defined(USE_AVX512)