Cleanup using C++17 features (#7931)

Small cleanup PR

Authors:
  - Conor Hoekstra (https://github.com/codereport)

Approvers:
  - Nghia Truong (https://github.com/ttnghia)
  - MithunR (https://github.com/mythrocks)

URL: #7931

cpp/include/cudf/ast/detail/transform.cuh

@@ -364,9 +364,7 @@ struct ast_plan {
   std::vector<cudf::size_type> get_offsets() const
   {
     auto offsets = std::vector<int>(sizes.size());
-    // When C++17, use std::exclusive_scan
-    offsets[0] = 0;
-    std::partial_sum(sizes.cbegin(), sizes.cend() - 1, offsets.begin() + 1);
+    thrust::exclusive_scan(sizes.cbegin(), sizes.cend(), offsets.begin(), 0);
     return offsets;
   }
 

cpp/include/cudf/detail/utilities/cuda.cuh

@@ -134,7 +134,7 @@ cudf::size_type elements_per_thread(Kernel kernel,
   int num_sms = 0;
   CUDA_TRY(cudaDeviceGetAttribute(&num_sms, cudaDevAttrMultiProcessorCount, device));
   int per_thread = total_size / (max_blocks * num_sms * block_size);
-  return std::max(1, std::min(per_thread, max_per_thread));  // switch to std::clamp with C++17
+  return std::clamp(per_thread, 1, max_per_thread);
 }
 
 /**

cpp/include/cudf_test/timestamp_utilities.cuh

@@ -55,11 +55,10 @@ inline cudf::test::fixed_width_column_wrapper<T, int64_t> generate_timestamps(in
   auto lhs = start.time_since_epoch().count();
   auto rhs = stop.time_since_epoch().count();
 
-  // When C++17, auto [min, max] = std::minmax(lhs, rhs)
-  auto min   = std::min(lhs, rhs);
-  auto max   = std::max(lhs, rhs);
-  auto range = max - min;
-  auto iter  = cudf::detail::make_counting_transform_iterator(0, [=](auto i) {
+  auto const min   = std::min(lhs, rhs);
+  auto const max   = std::max(lhs, rhs);
+  auto const range = max - min;
+  auto iter        = cudf::detail::make_counting_transform_iterator(0, [=](auto i) {
     return cuda::std::chrono::floor<ToDuration>(
              cuda::std::chrono::milliseconds(min + (range / count) * i))
       .count();

cpp/src/copying/contiguous_split.cu

@@ -660,10 +660,7 @@ BufInfo build_output_columns(InputIter begin,
 {
   auto current_info = info_begin;
   std::transform(begin, end, out_begin, [&current_info, base_ptr](column_view const& src) {
-    // Use C++17 structured bindings
-    bitmask_type const* bitmask_ptr;
-    size_type null_count;
-    std::tie(bitmask_ptr, null_count) = [&]() {
+    auto [bitmask_ptr, null_count] = [&]() {
       if (src.nullable()) {
         auto const ptr =
           current_info->num_elements == 0

cpp/src/io/json/reader_impl.cu

@@ -492,9 +492,8 @@ void reader::impl::set_data_types(rmm::cuda_stream_view stream)
                      std::cend(dtype),
                      std::inserter(col_type_map, col_type_map.end()),
                      [&](auto const &ts) -> std::pair<std::string, data_type> {
-                       // When C++17, use structured bindings: auto const& [col_name, type_str] = ..
-                       auto split = split_on_colon(ts);
-                       return {split.first, convert_string_to_dtype(split.second)};
+                       auto const &[col_name, type_str] = split_on_colon(ts);
+                       return {col_name, convert_string_to_dtype(type_str)};
                      });
 
       // Using the map here allows O(n log n) complexity

cpp/src/merge/merge.cu

@@ -297,7 +297,6 @@ struct column_merger {
                       row_order_.end(),
                       merged_view.begin<Element>(),
                       [d_lcol, d_rcol] __device__(index_type const& index_pair) {
-                        // When C++17, use structure bindings
                         auto side  = thrust::get<0>(index_pair);
                         auto index = thrust::get<1>(index_pair);
                         return side == side::LEFT ? d_lcol[index] : d_rcol[index];

cpp/tests/wrappers/timestamps_test.cu

@@ -83,10 +83,7 @@ TYPED_TEST(ChronoColumnTest, ChronoDurationsMatchPrimitiveRepresentation)
 
   // round-trip through the host to copy `chrono_col` values
   // to a new fixed_width_column_wrapper `primitive_col`
-  // When C++17, use structured bindings
-  thrust::host_vector<Rep> chrono_col_data;
-  std::vector<cudf::bitmask_type> chrono_col_mask;
-  std::tie(chrono_col_data, chrono_col_mask) = to_host<Rep>(chrono_col);
+  auto const [chrono_col_data, chrono_col_mask] = to_host<Rep>(chrono_col);
 
   auto primitive_col =
     fixed_width_column_wrapper<Rep>(chrono_col_data.begin(), chrono_col_data.end());