ranges: Add transform overload taking directly a pointer to member

This overload will forward to the general transform implementation
using std::mem_fn to generate a callable.

src/command_manager.cc

@@ -538,10 +538,10 @@ Completions CommandManager::complete_command_name(const Context& context, String
 {
     auto commands = m_commands
             | filter([](const CommandMap::Item& cmd) { return not (cmd.value.flags & CommandFlags::Hidden); })
-            | transform(std::mem_fn(&CommandMap::Item::key));
+            | transform(&CommandMap::Item::key);
 
     auto aliases = context.aliases().flatten_aliases()
-            | transform(std::mem_fn(&HashItem<String, String>::key))
+            | transform(&HashItem<String, String>::key)
             | filter([](auto& alias) { return alias.length() > 3; });
 
     return {0, query.length(), Kakoune::complete(query, query.length(), concatenated(commands, aliases))};

src/commands.cc

@@ -669,7 +669,7 @@ Completions highlighter_cmd_completer(
     else if (add and token_to_complete == 1)
     {
         StringView name = params[1];
-        return { 0_byte, name.length(), complete(name, pos_in_token, HighlighterRegistry::instance() | transform(std::mem_fn(&HighlighterRegistry::Item::key))) };
+        return { 0_byte, name.length(), complete(name, pos_in_token, HighlighterRegistry::instance() | transform(&HighlighterRegistry::Item::key)) };
     }
     else
         return {};
@@ -1593,7 +1593,7 @@ void context_wrap(const ParametersParser& parser, Context& context, Func func)
         if (*bufnames == "*")
         {
             for (auto&& buffer : BufferManager::instance()
-                               | transform(std::mem_fn(&std::unique_ptr<Buffer>::get))
+                               | transform(&std::unique_ptr<Buffer>::get)
                                | filter([](Buffer* buf) { return not (buf->flags() & Buffer::Flags::Debug); })
                                | gather<Vector<SafePtr<Buffer>>>()) // gather as we might be mutating the buffer list in the loop.
                 context_wrap_for_buffer(*buffer);

src/face_registry.cc

@@ -123,7 +123,7 @@ CandidateList FaceRegistry::complete_alias_name(StringView prefix,
                                                 ByteCount cursor_pos) const
 {
     return complete(prefix, cursor_pos,
-                    m_aliases | transform(std::mem_fn(&AliasMap::Item::key)));
+                    m_aliases | transform(&AliasMap::Item::key));
 }
 
 FaceRegistry::FaceRegistry()

src/highlighters.cc

@@ -1869,7 +1869,7 @@ public:
             return offset_pos(hl.complete_child(path.substr(offset), cursor_pos - offset, group), offset);
         }
 
-        auto container = m_groups | transform(std::mem_fn(&decltype(m_groups)::Item::key));
+        auto container = m_groups | transform(&decltype(m_groups)::Item::key);
         return { 0, 0, complete(path, cursor_pos, container) };
     }
 

src/main.cc

@@ -90,7 +90,7 @@ static const EnvVarDesc builtin_env_vars[] = { {
         "buflist", false,
         [](StringView name, const Context& context)
         { return join(BufferManager::instance() |
-                      transform(std::mem_fn(&Buffer::display_name)), ':'); }
+                      transform(&Buffer::display_name), ':'); }
     }, {
         "buf_line_count", false,
         [](StringView name, const Context& context) -> String

src/ncurses_ui.cc

@@ -731,7 +731,7 @@ void NCursesUI::menu_show(ConstArrayView<DisplayLine> items,
     const int item_count = items.size();
     m_menu.items.clear(); // make sure it is empty
     m_menu.items.reserve(item_count);
-    const auto longest = accumulate(items | transform(std::mem_fn(&DisplayLine::length)),
+    const auto longest = accumulate(items | transform(&DisplayLine::length),
                                     1_col, [](auto&& lhs, auto&& rhs) { return std::max(lhs, rhs); });
 
     const bool is_prompt = style == MenuStyle::Prompt;
@@ -945,7 +945,7 @@ void NCursesUI::info_show(StringView title, StringView content,
     }
 
     const DisplayCoord size{(int)info_box.size(),
-                            accumulate(info_box | transform(std::mem_fn(&String::column_length)), 0_col,
+                            accumulate(info_box | transform(&String::column_length), 0_col,
                                        [](auto&& lhs, auto&& rhs){ return std::max(lhs, rhs); })};
     const Rect rect = {m_status_on_top ? 1_line : 0_line, m_dimensions};
     DisplayCoord pos;

src/normal.cc

@@ -1200,7 +1200,7 @@ void select_object(Context& context, NormalParams params)
             { 'n', select_number },
             { 'u', select_argument },
         };
-        auto obj_it = find(selectors | transform(std::mem_fn(&ObjectType::key)), key).base();
+        auto obj_it = find(selectors | transform(&ObjectType::key), key).base();
         if (obj_it != std::end(selectors))
             return select_and_set_last<mode>(
                 context, std::bind(obj_it->func, _1, _2, count, flags));

src/option_manager.cc

@@ -109,7 +109,7 @@ CandidateList OptionsRegistry::complete_option_name(StringView prefix,
     return complete(prefix, cursor_pos, m_descs |
                     filter([](const OptionPtr& desc)
                            { return not (desc->flags() & OptionFlags::Hidden); }) |
-                    transform(std::mem_fn(&OptionDesc::name)));
+                    transform(&OptionDesc::name));
 }
 
 }

src/option_manager.hh

@@ -100,7 +100,7 @@ public:
         static const OptionMap empty;
         auto& parent = m_parent ? m_parent->m_options : empty;
         auto& grand_parent = (m_parent and m_parent->m_parent) ? m_parent->m_parent->m_options : empty;
-        return merge(merge(grand_parent, parent), m_options) | transform(std::mem_fn(&OptionMap::Item::value));
+        return merge(merge(grand_parent, parent), m_options) | transform(&OptionMap::Item::value);
     }
 
     void register_watcher(OptionManagerWatcher& watcher) const;

src/option_types.hh

@@ -30,7 +30,7 @@ option_type_name(Meta::Type<Enum>)
 {
     return format("{}({})", with_bit_ops(Meta::Type<Enum>{}) ? "flags" : "enum",
                   join(enum_desc(Meta::Type<Enum>{}) |
-                       transform(std::mem_fn(&EnumDesc<Enum>::name)), '|'));
+                       transform(&EnumDesc<Enum>::name), '|'));
 }
 
 inline String option_to_string(int opt) { return to_string(opt); }

src/ranges.hh

@@ -5,6 +5,7 @@
 #include <utility>
 #include <iterator>
 #include <numeric>
+#include <functional>
 
 #include "constexpr_utils.hh"
 
@@ -161,6 +162,12 @@ inline auto transform(Transform t)
     });
 }
 
+template<typename M, typename T>
+inline auto transform(M T::*m)
+{
+    return transform(std::mem_fn(std::forward<decltype(m)>(m)));
+}
+
 template<typename Range, bool escape = false,
          typename Element = ValueOf<Range>,
          typename ValueTypeParam = void>

src/shell_manager.cc

@@ -310,7 +310,7 @@ CandidateList ShellManager::complete_env_var(StringView prefix,
                                              ByteCount cursor_pos) const
 {
     return complete(prefix, cursor_pos,
-                    m_env_vars | transform(std::mem_fn(&EnvVarDesc::str)));
+                    m_env_vars | transform(&EnvVarDesc::str));
 }
 
 }