aboutsummaryrefslogtreecommitdiff
path: root/libbutl/small-list.hxx
diff options
context:
space:
mode:
Diffstat (limited to 'libbutl/small-list.hxx')
-rw-r--r--libbutl/small-list.hxx150
1 files changed, 150 insertions, 0 deletions
diff --git a/libbutl/small-list.hxx b/libbutl/small-list.hxx
new file mode 100644
index 0000000..aaeef22
--- /dev/null
+++ b/libbutl/small-list.hxx
@@ -0,0 +1,150 @@
+// file : libbutl/small-list.hxx -*- C++ -*-
+// license : MIT; see accompanying LICENSE file
+
+#pragma once
+
+#include <list>
+#include <cstddef> // size_t
+#include <utility> // move()
+
+#include <libbutl/small-allocator.hxx>
+
+#include <libbutl/export.hxx>
+
+namespace butl
+{
+ // Issues and limitations.
+ //
+ // - VC's implementation of std::list allocates an extra "headnode"
+ // (something to do with additional iterator stability guarantees). Which
+ // means only empty small list will actually be "small". As a result,
+ // unless you don't care about VC, you should use small_forward_list
+ // instead.
+ //
+ // - Because small_allocator currently expects us to allocate the entire
+ // small buffer and there is no reserve() in std::list, we currently
+ // only support N==1 (which we static_assert).
+ //
+ // - swap() is deleted (see notes below).
+ //
+ // - The implementation doesn't allocate T but rather a "node" that normally
+ // consists of two pointers (prev/next) and T.
+ //
+ template <typename T>
+ using small_list_node =
+#if defined (_MSC_VER)
+ std::_List_node<T, void*>;
+#elif defined (__GLIBCXX__)
+ std::_List_node<T>;
+#elif defined (_LIBCPP_VERSION)
+ std::__list_node<T, void*>;
+#else
+#error unknown standard library implementation
+#endif
+
+ template <typename T, std::size_t N>
+ using small_list_buffer = small_allocator_buffer<small_list_node<T>, N>;
+
+ template <typename T, std::size_t N>
+ class small_list:
+ private small_list_buffer<T, N>,
+ public std::list<T, small_allocator<T, N, small_list_buffer<T, N>>>
+ {
+ static_assert (N == 1, "only small_list or 1 currently supported");
+
+ public:
+ static constexpr const std::size_t small_size = N;
+
+ using buffer_type = small_list_buffer<T, N>;
+ using allocator_type = small_allocator<T, N, buffer_type>;
+ using base_type = std::list<T, allocator_type>;
+
+ small_list ()
+ : base_type (allocator_type (this)) {}
+
+ small_list (std::initializer_list<T> v)
+ : base_type (allocator_type (this))
+ {
+ static_cast<base_type&> (*this) = v;
+ }
+
+ template <typename I>
+ small_list (I b, I e)
+ : base_type (allocator_type (this))
+ {
+ this->assign (b, e);
+ }
+
+ explicit
+ small_list (std::size_t n)
+ : base_type (allocator_type (this))
+ {
+ this->resize (n);
+ }
+
+ small_list (std::size_t n, const T& x)
+ : base_type (allocator_type (this))
+ {
+ this->assign (n, x);
+ }
+
+ small_list (const small_list& v)
+ : buffer_type (), base_type (allocator_type (this))
+ {
+ static_cast<base_type&> (*this) = v;
+ }
+
+ small_list&
+ operator= (const small_list& v)
+ {
+ // Note: propagate_on_container_copy_assignment = false
+ //
+ static_cast<base_type&> (*this) = v;
+ return *this;
+ }
+
+ small_list (small_list&& v)
+ : base_type (allocator_type (this))
+ {
+ *this = std::move (v); // Delegate to operator=(&&).
+ }
+
+ small_list&
+ operator= (small_list&& v)
+ {
+ // libstdc++'s implementation prior to GCC 6 is broken (calls swap()).
+ // Since there is no easy way to determine this library's version, for
+ // now this is always enabled.
+ //
+ // Similarly, VC14's implementation of operator=(&&) swaps pointers
+ // without regard for allocator (fixed in 15).
+ //
+#if defined(__GLIBCXX__) || (defined(_MSC_VER) && _MSC_VER <= 1900)
+ this->clear ();
+ for (T& x: v)
+ this->push_back (std::move (x));
+ v.clear ();
+#else
+ // Note: propagate_on_container_move_assignment = false
+ //
+ static_cast<base_type&> (*this) = std::move (v);
+#endif
+
+ return *this;
+ }
+
+ small_list&
+ operator= (std::initializer_list<T> v)
+ {
+ static_cast<base_type&> (*this) = v;
+ return *this;
+ }
+
+ // Implementing swap() under small buffer optimization is not trivial, to
+ // say the least (think of swapping two such buffers of different sizes).
+ // One easy option would be to force both in to the heap.
+ //
+ void
+ swap (small_list&) = delete;
+ };
+}