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Subject: [Boost-commit] svn:boost r77905 - in trunk: boost/utility boost/utility/detail libs/utility libs/utility/test
From: eric_at_[hidden]
Date: 2012-04-10 20:28:34

Author: eric_niebler
Date: 2012-04-10 20:28:33 EDT (Tue, 10 Apr 2012)
New Revision: 77905
URL: http://svn.boost.org/trac/boost/changeset/77905

Log:
result_of uses decltype on compilers that implement N3276
Text files modified:
   trunk/boost/utility/detail/result_of_iterate.hpp | 6 ++--
   trunk/boost/utility/result_of.hpp | 18 +++++++++++++
   trunk/libs/utility/test/result_of_test.cpp | 6 +++
   trunk/libs/utility/utility.htm | 53 ++++++++++++++++++++++++---------------
   4 files changed, 59 insertions(+), 24 deletions(-)

Modified: trunk/boost/utility/detail/result_of_iterate.hpp
==============================================================================
--- trunk/boost/utility/detail/result_of_iterate.hpp (original)
+++ trunk/boost/utility/detail/result_of_iterate.hpp 2012-04-10 20:28:33 EDT (Tue, 10 Apr 2012)
@@ -38,7 +38,7 @@
(boost::detail::has_result_type<F>::value)> >::type { };
#endif

-#if !defined(BOOST_NO_DECLTYPE) && defined(BOOST_RESULT_OF_USE_DECLTYPE)
+#ifdef BOOST_RESULT_OF_USE_DECLTYPE

// Uses declval following N3225 20.7.7.6 when F is not a pointer.
template<typename F BOOST_PP_COMMA_IF(BOOST_PP_ITERATION())
@@ -71,7 +71,7 @@

} // namespace detail

-#else // defined(BOOST_NO_DECLTYPE)
+#else // defined(BOOST_RESULT_OF_USE_DECLTYPE)

#if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x551))
template<typename F BOOST_PP_COMMA_IF(BOOST_PP_ITERATION())
@@ -80,7 +80,7 @@
: tr1_result_of<F(BOOST_RESULT_OF_ARGS)> { };
#endif

-#endif // defined(BOOST_NO_DECLTYPE)
+#endif // defined(BOOST_RESULT_OF_USE_DECLTYPE)

#undef BOOST_RESULT_OF_ARGS

Modified: trunk/boost/utility/result_of.hpp
==============================================================================
--- trunk/boost/utility/result_of.hpp (original)
+++ trunk/boost/utility/result_of.hpp 2012-04-10 20:28:33 EDT (Tue, 10 Apr 2012)
@@ -30,6 +30,24 @@
# define BOOST_RESULT_OF_NUM_ARGS 16
#endif

+// Use the decltype-based version of result_of by default if the compiler
+// supports N3276 <http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2011/n3276.pdf>.
+// The user can force the choice by defining either BOOST_RESULT_OF_USE_DECLTYPE or
+// BOOST_RESULT_OF_USE_TR1, but not both!
+#if defined(BOOST_RESULT_OF_USE_DECLTYPE) && defined(BOOST_RESULT_OF_USE_TR1)
+# error Both BOOST_RESULT_OF_USE_DECLTYPE and BOOST_RESULT_OF_USE_TR1 cannot be defined at the same time.
+#endif
+
+#ifndef BOOST_RESULT_OF_USE_TR1
+# ifndef BOOST_RESULT_OF_USE_DECLTYPE
+# ifndef BOOST_NO_DECLTYPE_N3276 // this implies !defined(BOOST_NO_DECLTYPE)
+# define BOOST_RESULT_OF_USE_DECLTYPE
+# else
+# define BOOST_RESULT_OF_USE_TR1
+# endif
+# endif
+#endif
+
namespace boost {

template<typename F> struct result_of;

Modified: trunk/libs/utility/test/result_of_test.cpp
==============================================================================
--- trunk/libs/utility/test/result_of_test.cpp (original)
+++ trunk/libs/utility/test/result_of_test.cpp 2012-04-10 20:28:33 EDT (Tue, 10 Apr 2012)
@@ -5,7 +5,11 @@
// 1.0. (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)

-#define BOOST_RESULT_OF_USE_DECLTYPE
+#include <boost/config.hpp>
+
+#ifndef BOOST_NO_DECLTYPE
+# define BOOST_RESULT_OF_USE_DECLTYPE
+#endif

// For more information, see http://www.boost.org/libs/utility
#include <boost/utility/result_of.hpp>

Modified: trunk/libs/utility/utility.htm
==============================================================================
--- trunk/libs/utility/utility.htm (original)
+++ trunk/libs/utility/utility.htm 2012-04-10 20:28:33 EDT (Tue, 10 Apr 2012)
@@ -161,14 +161,12 @@
 resides in the header <code><<a
 href="../../boost/utility/result_of.hpp">boost/utility/result_of.hpp</a>></code>.

- If your compiler supports <code>decltype</code>,
- then you can enable automatic result type deduction by
- defining the macro <code>BOOST_RESULT_OF_USE_DECLTYPE</code>,
- as in the following example.
+ If your compiler's support for <code>decltype</code> is
+ adequate, <code>result_of</code> automatically uses it to
+ deduce the result type of your callable.

 <blockquote>
- <pre>#define BOOST_RESULT_OF_USE_DECLTYPE
-#include <boost/utility/result_of.hpp>
+ <pre>#include <boost/utility/result_of.hpp>

struct functor {
 template<class T>
@@ -180,21 +178,29 @@

typedef boost::result_of<
 functor(int)
->::type type;</pre>
+>::type type; // type is int</pre>
 </blockquote>

- If <code>decltype</code> is not enabled,
+ You can test whether <code>result_of</code> is using
+ <code>decltype</code> checking if the macro
+ <code>BOOST_RESULT_OF_USE_DECLTYPE</code> is defined after
+ including <code>result_of.hpp</code>. You can also force
+ <code>result_of</code> to use <code>decltype</code> by
+ defining <code>BOOST_RESULT_OF_USE_DECLTYPE</code> prior
+ to including <code>result_of.hpp</code>.
+
+ If <code>decltype</code> is not used,
 then automatic result type deduction of function
 objects is not possible. Instead, <code>result_of</code>
 uses the following protocol to allow the programmer to
 specify a type. When <code>F</code> is a class type with a
 member type <code>result_type</code>,
 <code>result_of<F(T1, T2, ...,
- TN)></code> is
+ TN)>::type</code> is
 <code>F::result_type</code>. When <code>F</code> does
 not contain <code>result_type</code>,
 <code>result_of<F(T1, T2, ...,
- TN)></code> is <code>F::result<F(T1,
+ TN)>::type</code> is <code>F::result<F(T1,
 T2, ..., TN)>::type</code> when
 <code>N > 0</code> or <code>void</code>
 when <code>N = 0</code>. Note that it is the
@@ -221,22 +227,29 @@

typedef boost::result_of<
 functor(int)
->::type type;</pre>
+>::type type; // type is int</pre>
 </blockquote>

- In a future
- release, <code>BOOST_RESULT_OF_USE_DECLTYPE</code>
- may be enabled by default on compilers that
- support <code>decltype</code>, so if you use the above
- protocol please take care to ensure that
- the <code>result_type</code>
- and <code>result<></code> members accurately
- represent the result type. If you wish to continue to
+ If you are writing a reusable function object
+ that should work with <code>result_of</code>, for
+ maximum portability, you might consider following
+ the above protocol even if your compiler has
+ proper <code>decltype</code> support. If you do,
+ take care to ensure that the
+ <code>result_type</code> and
+ <code>result<></code> members accurately
+ represent the return type of
+ <code>operator()</code>.
+
+ If you wish to continue to
 use the protocol on compilers that
 support <code>decltype</code>,
 use <code>boost::tr1_result_of</code>, which is also
 defined
- in <code><boost/utility/result_of.hpp></code>.
+ in <code><boost/utility/result_of.hpp></code>. You can also define the macro
+ <code>BOOST_RESULT_OF_USE_TR1</code>, which causes
+ <code>result_of</code> to use the convention described
+ above instead of <code>decltype</code>.

 <a name="BOOST_NO_RESULT_OF"></a>
 This implementation of <code>result_of</code>

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