From e68771df18fe874be1b97baf06f3d6841b122141 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=9B=D0=B5=D0=BE=D0=BD=D0=B8=D0=B4=20=D0=AE=D1=80=D1=8C?=
 =?UTF-8?q?=D0=B5=D0=B2=20=28Leonid=20Yuriev=29?= <leo@yuriev.ru>
Date: Sun, 26 Nov 2023 12:34:06 +0300
Subject: [PATCH] =?UTF-8?q?mdbx++:=20=D0=94=D0=BE=D0=B1=D0=B0=D0=B2=D0=BB?=
 =?UTF-8?q?=D0=B5=D0=BD=D0=B8=D0=B5=20`buffer=5Fpair<>`=20=D0=B8=20`buffer?=
 =?UTF-8?q?=5Fpair=5Fspec<>`.?=
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---
 mdbx.h++ | 86 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)

diff --git a/mdbx.h++ b/mdbx.h++
index d42b5942..74373039 100644
--- a/mdbx.h++
+++ b/mdbx.h++
@@ -3180,6 +3180,92 @@ struct pair_result : public pair {
   }
 };
 
+template <typename ALLOCATOR, typename CAPACITY_POLICY>
+struct buffer_pair_spec {
+  using buffer_type = buffer<ALLOCATOR, CAPACITY_POLICY>;
+  using allocator_type = typename buffer_type::allocator_type;
+  using allocator_traits = typename buffer_type::allocator_traits;
+  using reservation_policy = CAPACITY_POLICY;
+  using stl_pair = ::std::pair<buffer_type, buffer_type>;
+  buffer_type key, value;
+
+  MDBX_CXX20_CONSTEXPR buffer_pair_spec() noexcept = default;
+  MDBX_CXX20_CONSTEXPR
+  buffer_pair_spec(const allocator_type &allocator) noexcept
+      : key(allocator), value(allocator) {}
+
+  buffer_pair_spec(const buffer_type &key, const buffer_type &value,
+                   const allocator_type &allocator = allocator_type())
+      : key(key, allocator), value(value, allocator) {}
+  buffer_pair_spec(const buffer_type &key, const buffer_type &value,
+                   bool make_reference,
+                   const allocator_type &allocator = allocator_type())
+      : key(key, make_reference, allocator),
+        value(value, make_reference, allocator) {}
+
+  buffer_pair_spec(const stl_pair &pair,
+                   const allocator_type &allocator = allocator_type())
+      : buffer_pair_spec(pair.first, pair.second, allocator) {}
+  buffer_pair_spec(const stl_pair &pair, bool make_reference,
+                   const allocator_type &allocator = allocator_type())
+      : buffer_pair_spec(pair.first, pair.second, make_reference, allocator) {}
+
+  buffer_pair_spec(const slice &key, const slice &value,
+                   const allocator_type &allocator = allocator_type())
+      : key(key, allocator), value(value, allocator) {}
+  buffer_pair_spec(const slice &key, const slice &value, bool make_reference,
+                   const allocator_type &allocator = allocator_type())
+      : key(key, make_reference, allocator),
+        value(value, make_reference, allocator) {}
+
+  buffer_pair_spec(const pair &pair,
+                   const allocator_type &allocator = allocator_type())
+      : buffer_pair_spec(pair.key, pair.value, allocator) {}
+  buffer_pair_spec(const pair &pair, bool make_reference,
+                   const allocator_type &allocator = allocator_type())
+      : buffer_pair_spec(pair.key, pair.value, make_reference, allocator) {}
+
+  buffer_pair_spec(const txn &txn, const slice &key, const slice &value,
+                   const allocator_type &allocator = allocator_type())
+      : key(txn, key, allocator), value(txn, value, allocator) {}
+  buffer_pair_spec(const txn &txn, const pair &pair,
+                   const allocator_type &allocator = allocator_type())
+      : buffer_pair_spec(txn, pair.key, pair.value, allocator) {}
+
+  buffer_pair_spec(buffer_type &&key, buffer_type &&value) noexcept(
+      buffer_type::move_assign_alloc::is_nothrow())
+      : key(::std::move(key)), value(::std::move(value)) {}
+  buffer_pair_spec(buffer_pair_spec &&pair) noexcept(
+      buffer_type::move_assign_alloc::is_nothrow())
+      : buffer_pair_spec(::std::move(pair.key), ::std::move(pair.value)) {}
+
+  /// \brief Checks whether data chunk stored inside the buffers both, otherwise
+  /// at least one of buffers just refers to data located outside.
+  MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX20_CONSTEXPR bool
+  is_freestanding() const noexcept {
+    return key.is_freestanding() && value.is_freestanding();
+  }
+  /// \brief Checks whether one of the buffers just refers to data located
+  /// outside the buffer, rather than stores it.
+  MDBX_NOTHROW_PURE_FUNCTION MDBX_CXX20_CONSTEXPR bool
+  is_reference() const noexcept {
+    return key.is_reference() || value.is_reference();
+  }
+  /// \brief Makes buffers owning the data.
+  /// \details If buffer refers to an external data, then makes it the owner
+  /// of clone by allocating storage and copying the data.
+  void make_freestanding() {
+    key.make_freestanding();
+    value.make_freestanding();
+  }
+
+  operator pair() const noexcept { return pair(key, value); }
+};
+
+template <typename BUFFER>
+using buffer_pair = buffer_pair_spec<typename BUFFER::allocator_type,
+                                     typename BUFFER::reservation_policy>;
+
 /// end of cxx_data @}
 
 //------------------------------------------------------------------------------