[PATCH 5/5] news: c++: move semantics

[Akim Demaille]

---
 NEWS           | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++
 doc/bison.texi |  3 ---
 2 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/NEWS b/NEWS
index 47aa9cf1..b5d59626 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,58 @@ GNU Bison NEWS
 
 * Noteworthy changes in release ?.? (????-??-??) [?]
 
+** New features
+
+*** C++: Support for move semantics (lalr1.cc)
+
+  The lalr1.cc skeleton now fully supports C++ move semantics, while
+  maintaining compatibility with C++98.  You may now store move-only types
+  when using Bison's variants to store semantic values.  For instance:
+
+    %code {
+      #include <memory>
+      #include <vector>
+    }
+
+    %skeleton "lalr1.cc"
+    %define api.value.type variant
+
+    %%
+
+    %token <int> INT "int";
+    %nterm <std::unique_ptr<int>> int;
+    %nterm <std::vector<std::unique_ptr<int>>> list;
+
+    list:
+      %empty    {}
+    | list int  { $$ = std::move($1); $$.emplace_back(std::move($2)); }
+
+    int: "int"  { $$ = std::make_unique<int>($1); }
+
+*** C++: Implicit move of right-hand side values (lalr1.cc)
+
+  In modern C++ (C++11 and later), you should always use 'std::move' with
+  the values of the right-hand side symbols ($1, $2, etc.).  It is mandatory
+  for move-only types such as unique_ptr, and provides a significant speedup
+  for large types such as std::string, or std::vector, etc.
+
+  If '%define api.value.automove' is set, every occurrence '$n' is replaced
+  by 'std::move ($n)'.  The second rule in the previous grammar can be
+  simplified to:
+
+    list: list int  { $$ = $1; $$.emplace_back($2); }
+
+  A warning is issued when automove is enabled, and a value is used several
+  times.
+
+    input.yy:16.31-32: warning: multiple occurrences of $2 with 
api.value.automove enabled [-Wother]
+    exp: "twice" exp   { $$ = $2 + $2; }
+                                   ^^
+
+  Enabling api.value.automove does not require support for modern C++.  The
+  generated code is valid C++98/03, but will use copies instead of moves.
+
+  The new examples/variant-11.yy shows these features in action.
 
 * Noteworthy changes in release 3.1 (2018-08-27) [stable]
 
diff --git a/doc/bison.texi b/doc/bison.texi
index 3620c60f..3726854c 100644
--- a/doc/bison.texi
+++ b/doc/bison.texi
@@ -10705,9 +10705,6 @@ therefore, since, as far as we know, @code{double} is 
the most demanding
 type on all platforms, alignments are enforced for @code{double} whatever
 types are actually used.  This may waste space in some cases.
 
address@hidden
-Move semantics is not yet supported, but will soon be added.
-
 @item
 There might be portability issues we are not aware of.
 @end itemize
-- 
2.19.0