Fixing warnings about struct/class incompatibility

Author: gopal-msr

include/abstract_data_store.h

@@ -13,7 +13,7 @@
 namespace diskann
 {
 
-template <typename data_t> struct AbstractScratch;
+template <typename data_t> class AbstractScratch;
 
 template <typename data_t> class AbstractDataStore
 {

include/abstract_scratch.h

@@ -2,13 +2,14 @@
 namespace diskann
 {
 
-template <typename data_t> struct PQScratch;
+template <typename data_t> class PQScratch;
 
 // By somewhat more than a coincidence, it seems that both InMemQueryScratch
 // and SSDQueryScratch have the aligned query and PQScratch objects. So we
 // can put them in a neat hierarchy and keep PQScratch as a standalone class.
-template <typename data_t> struct AbstractScratch
+template <typename data_t> class AbstractScratch
 {
+  public:
     AbstractScratch() = default;
     // This class does not take any responsibilty for memory management of
     // its members. It is the responsibility of the derived classes to do so.

include/pq_scratch.h

@@ -6,8 +6,9 @@
 namespace diskann
 {
 
-template <typename T> struct PQScratch
+template <typename T> class PQScratch
 {
+  public:
     float *aligned_pqtable_dist_scratch = nullptr; // MUST BE AT LEAST [256 * NCHUNKS]
     float *aligned_dist_scratch = nullptr;         // MUST BE AT LEAST diskann MAX_DEGREE
     uint8_t *aligned_pq_coord_scratch = nullptr;   // AT LEAST  [N_CHUNKS * MAX_DEGREE]

include/quantized_distance.h

@@ -6,7 +6,7 @@
 
 namespace diskann
 {
-template <typename data_t> struct PQScratch;
+template <typename data_t> class PQScratch;
 
 template <typename data_t> class QuantizedDistance
 {

include/scratch.h

@@ -19,7 +19,7 @@
 
 namespace diskann
 {
-template <typename T> struct PQScratch;
+template <typename T> class PQScratch;
 
 //
 // AbstractScratch space for in-memory index based search