diff --git a/include/boost/utility/detail/result_of_iterate.hpp b/include/boost/utility/detail/result_of_iterate.hpp index 5cf30b6..29fcd78 100644 --- a/include/boost/utility/detail/result_of_iterate.hpp +++ b/include/boost/utility/detail/result_of_iterate.hpp @@ -38,7 +38,7 @@ struct tr1_result_of (boost::detail::has_result_type::value)> >::type { }; #endif -#ifdef BOOST_RESULT_OF_USE_DECLTYPE +#if !defined(BOOST_NO_DECLTYPE) && defined(BOOST_RESULT_OF_USE_DECLTYPE) // Uses declval following N3225 20.7.7.6 when F is not a pointer. template } // namespace detail -#else // defined(BOOST_RESULT_OF_USE_DECLTYPE) +#else // defined(BOOST_NO_DECLTYPE) #if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x551)) template : tr1_result_of { }; #endif -#endif // defined(BOOST_RESULT_OF_USE_DECLTYPE) +#endif // defined(BOOST_NO_DECLTYPE) #undef BOOST_RESULT_OF_ARGS diff --git a/include/boost/utility/result_of.hpp b/include/boost/utility/result_of.hpp index 93b7264..77c26fe 100644 --- a/include/boost/utility/result_of.hpp +++ b/include/boost/utility/result_of.hpp @@ -30,24 +30,6 @@ # define BOOST_RESULT_OF_NUM_ARGS 16 #endif -// Use the decltype-based version of result_of by default if the compiler -// supports N3276 . -// 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 struct result_of; diff --git a/utility.htm b/utility.htm index 65ead22..474a338 100644 --- a/utility.htm +++ b/utility.htm @@ -161,12 +161,14 @@ void f() { resides in the header <boost/utility/result_of.hpp>.

-

If your compiler's support for decltype is - adequate, result_of automatically uses it to - deduce the result type of your callable.

+

If your compiler supports decltype, + then you can enable automatic result type deduction by + defining the macro BOOST_RESULT_OF_USE_DECLTYPE, + as in the following example.

- 
#include <boost/utility/result_of.hpp>
+                
#define BOOST_RESULT_OF_USE_DECLTYPE
+#include <boost/utility/result_of.hpp>
 
 struct functor {
     template<class T>
@@ -178,29 +180,21 @@ struct functor {
 
 typedef boost::result_of<
     functor(int)
->::type type; // type is int

+>::type type;
-

You can test whether result_of is using - decltype checking if the macro - BOOST_RESULT_OF_USE_DECLTYPE is defined after - including result_of.hpp. You can also force - result_of to use decltype by - defining BOOST_RESULT_OF_USE_DECLTYPE prior - to including result_of.hpp.

- -

If decltype is not used, +

If decltype is not enabled, then automatic result type deduction of function objects is not possible. Instead, result_of uses the following protocol to allow the programmer to specify a type. When F is a class type with a member type result_type, result_of<F(T1, T2, ..., - TN)>::type is + TN)> is F::result_type. When F does not contain result_type, result_of<F(T1, T2, ..., - TN)>::type is F::result<F(T1, + TN)> is F::result<F(T1, T2, ..., TN)>::type when N > 0 or void when N = 0. Note that it is the @@ -227,29 +221,22 @@ typedef boost::result_of< typedef boost::result_of< functor(int) ->::type type; // type is int +>::type type; -

If you are writing a reusable function object - that should work with result_of, for - maximum portability, you might consider following - the above protocol even if your compiler has - proper decltype support. If you do, - take care to ensure that the - result_type and - result<> members accurately - represent the return type of - operator().

- -

If you wish to continue to +

In a future + release, BOOST_RESULT_OF_USE_DECLTYPE + may be enabled by default on compilers that + support decltype, so if you use the above + protocol please take care to ensure that + the result_type + and result<> members accurately + represent the result type. If you wish to continue to use the protocol on compilers that support decltype, use boost::tr1_result_of, which is also defined - in <boost/utility/result_of.hpp>. You can also define the macro - BOOST_RESULT_OF_USE_TR1, which causes - result_of to use the convention described - above instead of decltype.

+ in <boost/utility/result_of.hpp>.

This implementation of result_of