Fix return type of prefix increment overloads (rapidsai#14544)

Prefix increment operators should return a reference to the object. Some of our iterators don't return anything.
This PR fixes those iterators to be in line with what C++ expects.

Authors:
  - Vukasin Milovanovic (https://github.com/vuule)

Approvers:
  - Bradley Dice (https://github.com/bdice)
  - Nghia Truong (https://github.com/ttnghia)

URL: rapidsai#14544

cpp/src/copying/contiguous_split.cu

@@ -852,7 +852,11 @@ struct dst_offset_output_iterator {
 
   dst_offset_output_iterator operator+ __host__ __device__(int i) { return {c + i}; }
 
-  void operator++ __host__ __device__() { c++; }
+  dst_offset_output_iterator& operator++ __host__ __device__()
+  {
+    c++;
+    return *this;
+  }
 
   reference operator[] __device__(int i) { return dereference(c + i); }
   reference operator* __device__() { return dereference(c); }
@@ -873,13 +877,14 @@ struct dst_valid_count_output_iterator {
   using reference         = size_type&;
   using iterator_category = thrust::output_device_iterator_tag;
 
-  dst_valid_count_output_iterator operator+ __host__ __device__(int i)
+  dst_valid_count_output_iterator operator+ __host__ __device__(int i) { return {c + i}; }
+
+  dst_valid_count_output_iterator& operator++ __host__ __device__()
   {
-    return dst_valid_count_output_iterator{c + i};
+    c++;
+    return *this;
   }
 
-  void operator++ __host__ __device__() { c++; }
-
   reference operator[] __device__(int i) { return dereference(c + i); }
   reference operator* __device__() { return dereference(c); }
 

cpp/src/io/parquet/reader_impl_preprocess.cu

@@ -908,13 +908,14 @@ struct chunk_row_output_iter {
   using reference         = size_type&;
   using iterator_category = thrust::output_device_iterator_tag;
 
-  __host__ __device__ chunk_row_output_iter operator+(int i)
+  __host__ __device__ chunk_row_output_iter operator+(int i) { return {p + i}; }
+
+  __host__ __device__ chunk_row_output_iter& operator++()
   {
-    return chunk_row_output_iter{p + i};
+    p++;
+    return *this;
   }
 
-  __host__ __device__ void operator++() { p++; }
-
   __device__ reference operator[](int i) { return p[i].chunk_row; }
   __device__ reference operator*() { return p->chunk_row; }
 };
@@ -948,11 +949,14 @@ struct start_offset_output_iterator {
 
   constexpr start_offset_output_iterator operator+(size_t i)
   {
-    return start_offset_output_iterator{
-      pages, page_indices, cur_index + i, input_cols, max_depth, num_pages};
+    return {pages, page_indices, cur_index + i, input_cols, max_depth, num_pages};
   }
 
-  constexpr void operator++() { cur_index++; }
+  constexpr start_offset_output_iterator& operator++()
+  {
+    cur_index++;
+    return *this;
+  }
 
   __device__ reference operator[](size_t i) { return dereference(cur_index + i); }
   __device__ reference operator*() { return dereference(cur_index); }
@@ -1087,13 +1091,14 @@ struct page_offset_output_iter {
   using reference         = size_type&;
   using iterator_category = thrust::output_device_iterator_tag;
 
-  __host__ __device__ page_offset_output_iter operator+(int i)
+  __host__ __device__ page_offset_output_iter operator+(int i) { return {p, index + i}; }
+
+  __host__ __device__ page_offset_output_iter& operator++()
   {
-    return page_offset_output_iter{p, index + i};
+    index++;
+    return *this;
   }
 
-  __host__ __device__ void operator++() { index++; }
-
   __device__ reference operator[](int i) { return p[index[i]].str_offset; }
   __device__ reference operator*() { return p[*index].str_offset; }
 };