specify that merge input is to be treated as a const

Author: Gillgamesh

include/sketch/sketch_columns.h

@@ -34,7 +34,7 @@ class FixedSizeSketchColumn {
   void clear();
 
   void update(const vec_t update);
-  void merge(FixedSizeSketchColumn &other);
+  void merge(FixedSizeSketchColumn const& other);
   uint8_t get_depth() const;
   void serialize(std::ostream &binary_out) const;
 
@@ -98,7 +98,7 @@ class ResizeableSketchColumn {
   SketchSample<vec_t> sample() const;
   void clear();
   void update(const vec_t update);
-  void merge(ResizeableSketchColumn &other);
+  void merge(ResizeableSketchColumn const& other);
   uint8_t get_depth() const;
 
   [[deprecated]]
@@ -166,7 +166,7 @@ class ResizeableAlignedSketchColumn {
   SketchSample<vec_t> sample() const;
   void clear();
   void update(const vec_t update);
-  void merge(ResizeableAlignedSketchColumn &other);
+  void merge(ResizeableAlignedSketchColumn const& other);
   uint8_t get_depth() const;
 
   [[deprecated]]

src/sketch_columns.cpp

@@ -82,7 +82,7 @@ void FixedSizeSketchColumn::clear() {
   deterministic_bucket = {0, 0};
 }
 
-void FixedSizeSketchColumn::merge(FixedSizeSketchColumn &other) {
+void FixedSizeSketchColumn::merge(FixedSizeSketchColumn const& other) {
   for (size_t i = 0; i < capacity; ++i) {
     buckets[i] ^= other.buckets[i];
   }
@@ -202,7 +202,7 @@ void ResizeableSketchColumn::update(const vec_t update) {
   buckets[depth] ^= {update, checksum};
 }
 
-void ResizeableSketchColumn::merge(ResizeableSketchColumn &other) {
+void ResizeableSketchColumn::merge(ResizeableSketchColumn const& other) {
   deterministic_bucket ^= other.deterministic_bucket;
   if (other.capacity > capacity) {
     reallocate(other.capacity);
@@ -295,7 +295,7 @@ void ResizeableAlignedSketchColumn::update(const vec_t update) {
   aligned_buckets[depth] ^= {update, checksum};
 }
 
-void ResizeableAlignedSketchColumn::merge(ResizeableAlignedSketchColumn &other) {
+void ResizeableAlignedSketchColumn::merge(ResizeableAlignedSketchColumn const& other) {
   deterministic_bucket ^= other.deterministic_bucket;
   if (other.capacity > capacity) {
     reallocate(other.capacity);