fix sub_array and span in C++20 (#368)

.github/workflows/cov.yml

@@ -14,6 +14,10 @@ env:
   B2_OPTS: -q -j2 warnings-as-errors=on
   GCC_VERSION: 11
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref }}
+  cancel-in-progress: true
+
 jobs:
   cov:
     runs-on: macos-11

.github/workflows/fast.yml

@@ -20,6 +20,10 @@ on:
       - 'tools/**'
       - '*.md'
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref }}
+  cancel-in-progress: true
+
 jobs:
   cmake:
     runs-on: ${{ matrix.os }}

.github/workflows/slow.yml

@@ -10,6 +10,10 @@ on:
       - 'tools/**'
       - '*.md'
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref }}
+  cancel-in-progress: true
+
 env:
   B2_OPTS: -q -j2 warnings-as-errors=on
   UBSAN_OPTIONS: print_stacktrace=1

.github/workflows/superproject_cmake.yml

@@ -6,6 +6,10 @@ on:
       - master
       - develop
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref }}
+  cancel-in-progress: true
+
 jobs:
   build:
     runs-on: macos-latest

benchmark/CMakeLists.txt

@@ -28,8 +28,10 @@ function(add_benchmark NAME)
   add_executable(${NAME} ${SOURCE})
   target_include_directories(${NAME} PRIVATE ${__INCLUDE_DIRECTORIES})
   target_link_libraries(${NAME} PRIVATE Boost::histogram Boost::math benchmark_main ${__LINK_LIBRARIES})
-  target_compile_options(${NAME} PRIVATE -DNDEBUG -O3 -march=native -funsafe-math-optimizations ${__COMPILE_OPTIONS})
-
+  target_compile_options(${NAME} PRIVATE -DNDEBUG -O3 -funsafe-math-optimizations ${__COMPILE_OPTIONS})
+  if (NOT DARWIN)
+    target_compile_options(${NAME} PRIVATE -march=native)
+  endif()
 endfunction()
 
 add_benchmark(axis_size)

benchmark/histogram_parallel_filling.cpp

@@ -50,12 +50,12 @@ static auto hist = make_histogram_with(DSTS(), axis::regular<>());
 
 static void AtomicStorage(benchmark::State& state) {
   init.lock();
-  if (state.thread_index == 0) {
+  if (state.thread_index() == 0) {
     const unsigned nbins = state.range(0);
     hist = make_histogram_with(DSTS(), axis::regular<>(nbins, 0, 1));
   }
   init.unlock();
-  std::default_random_engine gen(state.thread_index);
+  std::default_random_engine gen(state.thread_index());
   std::uniform_real_distribution<> dis(0, 1);
   for (auto _ : state) {
     // simulate some work

include/boost/histogram/detail/span.hpp

@@ -7,31 +7,6 @@
 #ifndef BOOST_HISTOGRAM_DETAIL_SPAN_HPP
 #define BOOST_HISTOGRAM_DETAIL_SPAN_HPP
 
-#ifdef __has_include
-#if __has_include(<version>)
-#include <version>
-#ifdef __cpp_lib_span
-#if __cpp_lib_span >= 201902
-#define BOOST_HISTOGRAM_DETAIL_HAS_STD_SPAN
-#endif
-#endif
-#endif
-#endif
-
-#ifdef BOOST_HISTOGRAM_DETAIL_HAS_STD_SPAN
-
-#include <span>
-
-namespace boost {
-namespace histogram {
-namespace detail {
-using std::span;
-} // namespace detail
-} // namespace histogram
-} // namespace boost
-
-#else // C++17 span not available, so we use our implementation
-
 // to be replaced by boost::span
 
 #include <array>
@@ -238,8 +213,6 @@ public:
 } // namespace histogram
 } // namespace boost
 
-#endif
-
 #include <boost/histogram/detail/nonmember_container_access.hpp>
 #include <utility>
 

include/boost/histogram/detail/sub_array.hpp

@@ -15,15 +15,17 @@ namespace boost {
 namespace histogram {
 namespace detail {
 
+// Like std::array, but allows to use less than maximum capacity.
+// Cannot inherit from std::array, since this confuses span.
 template <class T, std::size_t N>
 class sub_array {
-  constexpr bool swap_element_is_noexcept() noexcept {
+  static constexpr bool swap_element_is_noexcept() noexcept {
     using std::swap;
     return noexcept(swap(std::declval<T&>(), std::declval<T&>()));
   }
 
 public:
-  using value_type = T;
+  using element_type = T;
   using size_type = std::size_t;
   using reference = T&;
   using const_reference = const T&;
@@ -42,6 +44,12 @@ public:
     fill(value);
   }
 
+  sub_array(std::initializer_list<T> il) noexcept(
+      std::is_nothrow_assignable<T, const_reference>::value)
+      : sub_array(il.size()) {
+    std::copy(il.begin(), il.end(), data_);
+  }
+
   reference at(size_type pos) noexcept {
     if (pos >= size()) BOOST_THROW_EXCEPTION(std::out_of_range{"pos is out of range"});
     return data_[pos];
@@ -70,10 +78,7 @@ public:
   iterator end() noexcept { return begin() + size_; }
   const_iterator end() const noexcept { return begin() + size_; }
 
-  const_iterator cbegin() noexcept { return data_; }
   const_iterator cbegin() const noexcept { return data_; }
-
-  const_iterator cend() noexcept { return cbegin() + size_; }
   const_iterator cend() const noexcept { return cbegin() + size_; }
 
   constexpr size_type max_size() const noexcept { return N; }
@@ -87,17 +92,20 @@ public:
 
   void swap(sub_array& other) noexcept(swap_element_is_noexcept()) {
     using std::swap;
-    for (auto i = begin(), j = other.begin(); i != end(); ++i, ++j) swap(*i, *j);
+    const size_type s = (std::max)(size(), other.size());
+    for (auto i = begin(), j = other.begin(), end = begin() + s; i != end; ++i, ++j)
+      swap(*i, *j);
+    swap(size_, other.size_);
   }
 
 private:
   size_type size_ = 0;
-  value_type data_[N];
+  element_type data_[N];
 };
 
 template <class T, std::size_t N>
 bool operator==(const sub_array<T, N>& a, const sub_array<T, N>& b) noexcept {
-  return std::equal(a.begin(), a.end(), b.begin());
+  return std::equal(a.begin(), a.end(), b.begin(), b.end());
 }
 
 template <class T, std::size_t N>

test/CMakeLists.txt

@@ -73,6 +73,7 @@ boost_test(TYPE run SOURCES detail_operators_test.cpp)
 boost_test(TYPE run SOURCES detail_relaxed_equal_test.cpp)
 boost_test(TYPE run SOURCES detail_replace_type_test.cpp)
 boost_test(TYPE run SOURCES detail_safe_comparison_test.cpp)
+boost_test(TYPE run SOURCES detail_sub_array_and_span_test.cpp)
 boost_test(TYPE run SOURCES detail_static_if_test.cpp)
 boost_test(TYPE run SOURCES detail_tuple_slice_test.cpp)
 boost_test(TYPE run SOURCES histogram_custom_axis_test.cpp)

test/Jamfile

@@ -77,6 +77,7 @@ alias cxx14 :
     [ run detail_replace_type_test.cpp ]
     [ run detail_safe_comparison_test.cpp ]
     [ run detail_static_if_test.cpp ]
+    [ run detail_sub_array_and_span_test.cpp ]
     [ run detail_tuple_slice_test.cpp ]
     [ run histogram_custom_axis_test.cpp ]
     [ run histogram_dynamic_test.cpp ]

test/detail_misc_test.cpp

@@ -126,22 +126,6 @@ int main() {
     BOOST_TEST_EQ(count, 6);
   }
 
-  // sub_array and span
-  {
-    dtl::sub_array<int, 2> a(2, 1);
-    a[1] = 2;
-    auto sp = dtl::span<int>(a);
-    BOOST_TEST_EQ(sp.size(), 2);
-    BOOST_TEST_EQ(sp.front(), 1);
-    BOOST_TEST_EQ(sp.back(), 2);
-
-    const auto& ca = a;
-    auto csp = dtl::span<const int>(ca);
-    BOOST_TEST_EQ(csp.size(), 2);
-    BOOST_TEST_EQ(csp.front(), 1);
-    BOOST_TEST_EQ(csp.back(), 2);
-  }
-
   // index_translator
   {
     using I = axis::integer<>;

test/detail_sub_array_and_span_test.cpp

@@ -0,0 +1,87 @@
+#include <boost/core/lightweight_test.hpp>
+#include <boost/histogram/detail/nonmember_container_access.hpp>
+#include <boost/histogram/detail/reduce_command.hpp>
+#include <boost/histogram/detail/span.hpp>
+#include <boost/histogram/detail/sub_array.hpp>
+#include <initializer_list>
+#include <stdexcept>
+#include <utility>
+#include "throw_exception.hpp"
+
+namespace boost {
+namespace histogram {
+namespace detail {
+template <class T, std::size_t N>
+std::ostream& operator<<(std::ostream& os, const sub_array<T, N>&) {
+  return os;
+}
+std::ostream& operator<<(std::ostream& os, const reduce_command&) { return os; }
+} // namespace detail
+} // namespace histogram
+} // namespace boost
+
+using namespace boost::histogram::detail;
+
+int main() {
+
+  {
+    sub_array<int, 3> a = {1, 2};
+
+    BOOST_TEST_EQ(a.size(), 2);
+    BOOST_TEST_EQ(a.max_size(), 3);
+    BOOST_TEST_EQ(a.at(0), 1);
+    BOOST_TEST_EQ(a.at(1), 2);
+
+    sub_array<int, 3> b = {1, 2};
+    BOOST_TEST_EQ(a, b);
+
+    sub_array<int, 3> c = {1, 2, 3};
+    BOOST_TEST_NE(a, c);
+
+    sub_array<int, 3> d = {2, 2};
+    BOOST_TEST_NE(a, d);
+
+    auto sp = span<int>(a);
+    BOOST_TEST_EQ(sp.size(), 2);
+    BOOST_TEST_EQ(sp.front(), 1);
+    BOOST_TEST_EQ(sp.back(), 2);
+
+    const auto& ca = a;
+    auto csp = span<const int>(ca);
+    BOOST_TEST_EQ(csp.size(), 2);
+    BOOST_TEST_EQ(csp.front(), 1);
+    BOOST_TEST_EQ(csp.back(), 2);
+  }
+
+  {
+    sub_array<int, 2> a(2, 1);
+    sub_array<int, 2> b(1, 2);
+    std::swap(a, b);
+
+    BOOST_TEST_EQ(a.size(), 1);
+    BOOST_TEST_EQ(b.size(), 2);
+    BOOST_TEST_EQ(a[0], 2);
+    BOOST_TEST_EQ(b[0], 1);
+    BOOST_TEST_EQ(b[1], 1);
+  }
+
+  {
+    const std::initializer_list<int> a = {1, 2};
+    auto sp = span<const int>(a);
+    BOOST_TEST_EQ(sp.size(), 2);
+  }
+
+  {
+    const sub_array<reduce_command, 3> a(2);
+    auto sp = span<const reduce_command>(a);
+    BOOST_TEST_EQ(sp.size(), 2);
+  }
+
+  {
+    const std::initializer_list<reduce_command> a = {reduce_command{}};
+    auto sp = span<const reduce_command>(a);
+    BOOST_TEST_EQ(sp.size(), 1);
+  }
+
+  return boost::report_errors();
+}