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c++: prefer a perfect forwarding version of variant's emplace
From: |
Akim Demaille |
Subject: |
c++: prefer a perfect forwarding version of variant's emplace |
Date: |
Sat, 20 Oct 2018 19:09:07 +0200 |
commit 3ead69b1c1241100b7a2d2b6c6fd89d545c23ca4
Author: Akim Demaille <address@hidden>
Date: Sat Oct 20 14:25:45 2018 +0200
c++: prefer a perfect forwarding version of variant's emplace
* data/variant.hh (emplace): In modern C++, use only a perfect
forwarding version.
And use it.
* doc/bison.texi: Document it.
diff --git a/data/variant.hh b/data/variant.hh
index 089e04fa..5cc3df11 100644
--- a/data/variant.hh
+++ b/data/variant.hh
@@ -125,6 +125,18 @@ m4_define([b4_variant_define],
return *new (yyas_<T> ()) T ();
}
+# if defined __cplusplus && 201103L <= __cplusplus
+ /// Instantiate a \a T in here from \a t.
+ template <typename T, typename U>
+ T&
+ emplace (U&& u)
+ {]b4_parse_assert_if([
+ YYASSERT (!yytypeid_);
+ YYASSERT (sizeof (T) <= S);
+ yytypeid_ = & typeid (T);])[
+ return *new (yyas_<T> ()) T (std::forward <U>(u));
+ }
+# else
/// Instantiate a \a T in here from \a t.
template <typename T>
T&
@@ -135,6 +147,7 @@ m4_define([b4_variant_define],
yytypeid_ = & typeid (T);])[
return *new (yyas_<T> ()) T (t);
}
+# endif
/// Instantiate an empty \a T in here.
/// Obsolete, use emplace.
@@ -200,10 +213,10 @@ m4_define([b4_variant_define],
void
move (self_type& other)
{
- emplace<T> ();
# if defined __cplusplus && 201103L <= __cplusplus
- as<T> () = std::move (other.as<T> ());
+ emplace<T> (std::move (other.as<T> ()));
# else
+ emplace<T> ();
swap<T> (other);
# endif
other.destroy<T> ();
@@ -215,8 +228,7 @@ m4_define([b4_variant_define],
void
move (self_type&& other)
{
- emplace<T> ();
- as<T> () = std::move (other.as<T> ());
+ emplace<T> (std::move (other.as<T> ()));
other.destroy<T> ();
}
#endif
diff --git a/doc/bison.texi b/doc/bison.texi
index fcee42fe..00c59a37 100644
--- a/doc/bison.texi
+++ b/doc/bison.texi
@@ -10836,12 +10836,17 @@ in midrule actions. It is mandatory to use typed
midrule actions
(@pxref{Typed Midrule Actions}).
@deftypemethod {semantic_type} {T&} emplace<T> ()
-Initialize, but leave empty. Returns the address where the actual value may
-be stored. Requires that the variant was not initialized yet.
+Initialize, but leave empty. Return a reference to where the actual value
+may be stored. Requires that the variant was not initialized yet.
@end deftypemethod
@deftypemethod {semantic_type} {T&} emplace<T> (const T& @var{t})
-Initialize, and copy-construct from @var{t}.
+Initialize, and copy-construct from @var{t}. Available in C++98/C++03 only.
address@hidden deftypemethod
+
address@hidden {semantic_type} {T&} emplace<T, U> (U&& @var{u})
+Build a variant of type @code{T} from the forwarding reference @var{u}.
+Available in C++11 and later only.
@end deftypemethod
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