From 89e2a96369109f9863e369b30770600383750324 Mon Sep 17 00:00:00 2001
From: Patrick Stotko <stotko@cs.uni-bonn.de>
Date: Wed, 17 Jul 2024 08:10:39 +0200
Subject: [PATCH] utility: Add custom pair implementation

---
 examples/cuda/unordered_map.cu    |   3 +-
 examples/openmp/unordered_map.cpp |   3 +-
 src/stdgpu/impl/utility_detail.h  | 100 ++++++++++++++++++++
 src/stdgpu/utility.h              | 150 +++++++++++++++++++++++++++++-
 4 files changed, 252 insertions(+), 4 deletions(-)

diff --git a/examples/cuda/unordered_map.cu b/examples/cuda/unordered_map.cu
index 09e9aee3a..06bf2c3e2 100644
--- a/examples/cuda/unordered_map.cu
+++ b/examples/cuda/unordered_map.cu
@@ -104,7 +104,8 @@ main()
     stdgpu::pair<int, int> sum =
             thrust::reduce(range_map.begin(), range_map.end(), stdgpu::pair<int, int>(0, 0), int_pair_plus());
 
-    const stdgpu::pair<int, int> sum_closed_form = { n * (n + 1) / 2, n * (n + 1) * (2 * n + 1) / 6 };
+    const stdgpu::pair<int, int> sum_closed_form = { static_cast<int>(n * (n + 1) / 2),
+                                                     static_cast<int>(n * (n + 1) * (2 * n + 1) / 6) };
 
     std::cout << "The duplicate-free map of numbers contains " << map.size() << " elements (" << n + 1
               << " expected) and the computed sums are (" << sum.first << ", " << sum.second << ") (("
diff --git a/examples/openmp/unordered_map.cpp b/examples/openmp/unordered_map.cpp
index 3a61735c1..2ebc4a579 100644
--- a/examples/openmp/unordered_map.cpp
+++ b/examples/openmp/unordered_map.cpp
@@ -100,7 +100,8 @@ main()
     stdgpu::pair<int, int> sum =
             thrust::reduce(range_map.begin(), range_map.end(), stdgpu::pair<int, int>(0, 0), int_pair_plus());
 
-    const stdgpu::pair<int, int> sum_closed_form = { n * (n + 1) / 2, n * (n + 1) * (2 * n + 1) / 6 };
+    const stdgpu::pair<int, int> sum_closed_form = { static_cast<int>(n * (n + 1) / 2),
+                                                     static_cast<int>(n * (n + 1) * (2 * n + 1) / 6) };
 
     std::cout << "The duplicate-free map of numbers contains " << map.size() << " elements (" << n + 1
               << " expected) and the computed sums are (" << sum.first << ", " << sum.second << ") (("
diff --git a/src/stdgpu/impl/utility_detail.h b/src/stdgpu/impl/utility_detail.h
index a913768d6..748802ca7 100644
--- a/src/stdgpu/impl/utility_detail.h
+++ b/src/stdgpu/impl/utility_detail.h
@@ -19,6 +19,106 @@
 namespace stdgpu
 {
 
+template <typename T1, typename T2>
+template <
+        STDGPU_DETAIL_OVERLOAD_DEFINITION_IF(std::is_default_constructible_v<T1>&& std::is_default_constructible_v<T2>)>
+constexpr STDGPU_HOST_DEVICE
+pair<T1, T2>::pair()
+  : first()
+  , second()
+{
+}
+
+template <typename T1, typename T2>
+template <STDGPU_DETAIL_OVERLOAD_DEFINITION_IF(std::is_copy_constructible_v<T1>&& std::is_copy_constructible_v<T2>)>
+constexpr STDGPU_HOST_DEVICE
+pair<T1, T2>::pair(const T1& x, const T2& y)
+  : first(x)
+  , second(y)
+{
+}
+
+template <typename T1, typename T2>
+template <class U1,
+          class U2,
+          STDGPU_DETAIL_OVERLOAD_DEFINITION_IF(std::is_constructible_v<T1, U1>&& std::is_constructible_v<T2, U2>)>
+constexpr STDGPU_HOST_DEVICE
+pair<T1, T2>::pair(U1&& x, U2&& y)
+  : first(forward<U1>(x))
+  , second(forward<U2>(y))
+{
+}
+
+template <typename T1, typename T2>
+template <typename U1,
+          typename U2,
+          STDGPU_DETAIL_OVERLOAD_DEFINITION_IF(std::is_constructible_v<T1, U1&>&& std::is_constructible_v<T2, U2&>)>
+constexpr STDGPU_HOST_DEVICE
+pair<T1, T2>::pair(pair<U1, U2>& p)
+  : first(p.first)
+  , second(p.second)
+{
+}
+
+template <typename T1, typename T2>
+template <typename U1,
+          typename U2,
+          STDGPU_DETAIL_OVERLOAD_DEFINITION_IF(
+                  std::is_constructible_v<T1, const U1&>&& std::is_constructible_v<T2, const U2&>)>
+constexpr STDGPU_HOST_DEVICE
+pair<T1, T2>::pair(const pair<U1, U2>& p)
+  : first(p.first)
+  , second(p.second)
+{
+}
+
+template <typename T1, typename T2>
+template <typename U1,
+          typename U2,
+          STDGPU_DETAIL_OVERLOAD_DEFINITION_IF(std::is_constructible_v<T1, U1>&& std::is_constructible_v<T2, U2>)>
+constexpr STDGPU_HOST_DEVICE
+pair<T1, T2>::pair(pair<U1, U2>&& p)
+  : first(forward<U1>(p.first))
+  , second(forward<U2>(p.second))
+{
+}
+
+template <typename T1, typename T2>
+template <typename U1,
+          typename U2,
+          STDGPU_DETAIL_OVERLOAD_DEFINITION_IF(std::is_constructible_v<T1, U1>&& std::is_constructible_v<T2, U2>)>
+constexpr STDGPU_HOST_DEVICE
+pair<T1, T2>::pair(const pair<U1, U2>&& p)
+  : first(forward<const U1>(p.first))
+  , second(forward<const U2>(p.second))
+{
+}
+
+template <typename T1, typename T2>
+template <class U1,
+          class U2,
+          STDGPU_DETAIL_OVERLOAD_DEFINITION_IF(
+                  std::is_assignable_v<T1&, const U1&>&& std::is_assignable_v<T2&, const U2&>)>
+constexpr STDGPU_HOST_DEVICE pair<T1, T2>&
+pair<T1, T2>::operator=(const pair<U1, U2>& p)
+{
+    first = p.first;
+    second = p.second;
+    return *this;
+}
+
+template <typename T1, typename T2>
+template <class U1,
+          class U2,
+          STDGPU_DETAIL_OVERLOAD_DEFINITION_IF(std::is_assignable_v<T1&, U1>&& std::is_assignable_v<T2&, U2>)>
+constexpr STDGPU_HOST_DEVICE pair<T1, T2>&
+pair<T1, T2>::operator=(pair<U1, U2>&& p)
+{
+    first = forward<U1>(p.first);
+    second = forward<U1>(p.second);
+    return *this;
+}
+
 template <class T>
 constexpr STDGPU_HOST_DEVICE T&&
 forward(std::remove_reference_t<T>& t) noexcept
diff --git a/src/stdgpu/utility.h b/src/stdgpu/utility.h
index 61e697e5b..04c2afae5 100644
--- a/src/stdgpu/utility.h
+++ b/src/stdgpu/utility.h
@@ -25,10 +25,10 @@
  * \file stdgpu/utility.h
  */
 
-#include <thrust/pair.h>
 #include <type_traits>
 
 #include <stdgpu/platform.h>
+#include <stdgpu/type_traits.h>
 
 namespace stdgpu
 {
@@ -40,7 +40,153 @@ namespace stdgpu
  * \brief A pair of two values of potentially different types
  */
 template <typename T1, typename T2>
-using pair = thrust::pair<T1, T2>;
+struct pair
+{
+    using first_type = T1;  /**< T1 */
+    using second_type = T2; /**< T2 */
+
+    /**
+     * \brief Default Destructor
+     */
+    ~pair() = default;
+
+    /**
+     * \brief Constructor
+     */
+    template <STDGPU_DETAIL_OVERLOAD_IF(std::is_default_constructible_v<T1>&& std::is_default_constructible_v<T2>)>
+    constexpr STDGPU_HOST_DEVICE
+    pair();
+
+    /**
+     * \brief Constructor
+     * \param[in] x The new first element
+     * \param[in] y The new second element
+     */
+    template <STDGPU_DETAIL_OVERLOAD_IF(std::is_copy_constructible_v<T1>&& std::is_copy_constructible_v<T2>)>
+    constexpr STDGPU_HOST_DEVICE
+    pair(const T1& x, const T2& y);
+
+    /**
+     * \brief Constructor
+     * \tparam U1 The type of the first element
+     * \tparam U2 The type of the second element
+     * \param[in] x The new first element
+     * \param[in] y The new second element
+     */
+    template <class U1 = T1,
+              class U2 = T2,
+              STDGPU_DETAIL_OVERLOAD_IF(std::is_constructible_v<T1, U1>&& std::is_constructible_v<T2, U2>)>
+    constexpr STDGPU_HOST_DEVICE
+    pair(U1&& x, U2&& y);
+
+    /**
+     * \brief Copy constructor
+     * \tparam U1 The type of the other pair's first element
+     * \tparam U2 The type of the other pair's second element
+     * \param[in] p The pair to copy from
+     */
+    template <typename U1,
+              typename U2,
+              STDGPU_DETAIL_OVERLOAD_IF(std::is_constructible_v<T1, U1&>&& std::is_constructible_v<T2, U2&>)>
+    constexpr STDGPU_HOST_DEVICE
+    pair(pair<U1, U2>& p); // NOLINT(hicpp-explicit-conversions)
+
+    /**
+     * \brief Copy constructor
+     * \tparam U1 The type of the other pair's first element
+     * \tparam U2 The type of the other pair's second element
+     * \param[in] p The copied pair
+     */
+    template <
+            typename U1,
+            typename U2,
+            STDGPU_DETAIL_OVERLOAD_IF(std::is_constructible_v<T1, const U1&>&& std::is_constructible_v<T2, const U2&>)>
+    constexpr STDGPU_HOST_DEVICE
+    pair(const pair<U1, U2>& p); // NOLINT(hicpp-explicit-conversions)
+
+    /**
+     * \brief Move constructor
+     * \tparam U1 The type of the other pair's first element
+     * \tparam U2 The type of the other pair's second element
+     * \param[in] p The moved pair
+     */
+    template <class U1,
+              class U2,
+              STDGPU_DETAIL_OVERLOAD_IF(std::is_constructible_v<T1, U1>&& std::is_constructible_v<T2, U2>)>
+    constexpr STDGPU_HOST_DEVICE
+    pair(pair<U1, U2>&& p); // NOLINT(hicpp-explicit-conversions)
+
+    /**
+     * \brief Move constructor
+     * \tparam U1 The type of the other pair's first element
+     * \tparam U2 The type of the other pair's second element
+     * \param[in] p The moved pair
+     */
+    template <class U1,
+              class U2,
+              STDGPU_DETAIL_OVERLOAD_IF(std::is_constructible_v<T1, U1>&& std::is_constructible_v<T2, U2>)>
+    constexpr STDGPU_HOST_DEVICE
+    pair(const pair<U1, U2>&& p); // NOLINT(hicpp-explicit-conversions)
+
+    /**
+     * \brief Default copy constructor
+     * \param[in] p The copied pair
+     */
+    pair(const pair& p) = default;
+
+    /**
+     * \brief Default move constructor
+     * \param[in] p The moved pair
+     */
+    pair(pair&& p) = default; // NOLINT(hicpp-noexcept-move,performance-noexcept-move-constructor)
+
+    /**
+     * \brief Default copy assignment operator
+     * \param[in] p The pair to copy from
+     * \return *this
+     */
+    pair&
+    operator=(const pair& p) = default;
+
+    /**
+     * \brief Copy assignment operator
+     * \tparam U1 The type of the other pair's first element
+     * \tparam U2 The type of the other pair's second element
+     * \param[in] p The pair to copy from
+     * \return *this
+     */
+    template <class U1,
+              class U2,
+              STDGPU_DETAIL_OVERLOAD_IF(std::is_assignable_v<T1&, const U1&>&& std::is_assignable_v<T2&, const U2&>)>
+    constexpr STDGPU_HOST_DEVICE pair&
+    operator=(const pair<U1, U2>& p);
+
+    /**
+     * \brief Default move assignment operator
+     * \param[in] p The moved pair
+     * \return *this
+     */
+    pair&
+    operator=(pair&& p) = default; // NOLINT(hicpp-noexcept-move,performance-noexcept-move-constructor)
+
+    /**
+     * \brief Move assignment operator
+     * \tparam U1 The type of the other pair's first element
+     * \tparam U2 The type of the other pair's second element
+     * \param[in] p The moved pair
+     * \return *this
+     */
+    template <class U1,
+              class U2,
+              STDGPU_DETAIL_OVERLOAD_IF(std::is_assignable_v<T1&, U1>&& std::is_assignable_v<T2&, U2>)>
+    constexpr STDGPU_HOST_DEVICE pair&
+    operator=(pair<U1, U2>&& p);
+
+    // NOLINTNEXTLINE(misc-non-private-member-variables-in-classes)
+    first_type first; /**< First element of pair */
+    // NOLINTNEXTLINE(misc-non-private-member-variables-in-classes)
+    second_type second; /**< Second element of pair */
+};
 
 /**
  * \ingroup utility