result_of implementation that makes use of C++0x decltype, from Daniel Walker. Fixes #862.

[SVN r45256]

include/boost/utility/detail/result_of_iterate.hpp

@@ -10,6 +10,46 @@
 # error Boost result_of - do not include this file!
 #endif
 
+#if defined(BOOST_HAS_DECLTYPE)
+
+// As of N2588, C++0x result_of only supports function call
+// expressions of the form f(x). This precludes support for member
+// function pointers, which are invoked with expressions of the form
+// o->*f(x). This implementation supports both.
+template<typename F BOOST_PP_COMMA_IF(BOOST_PP_ITERATION())
+         BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),typename T)>
+struct result_of<F(BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T))>
+    : mpl::if_<
+          mpl::or_< is_pointer<F>, is_member_function_pointer<F> >
+        , detail::result_of_impl<
+              F, F(BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T)), false
+          >
+        , detail::result_of_decltype_impl<
+              F(BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T))
+          >
+      >::type
+{};
+
+namespace detail {
+
+# define BOOST_RESULT_OF_STATIC_MEMBERS(z, n, _) \
+     static T ## n t ## n; \
+  /**/
+
+template<typename F BOOST_PP_COMMA_IF(BOOST_PP_ITERATION())
+         BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),typename T)>
+class result_of_decltype_impl<F(BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),T))>
+{
+  static F f;
+  BOOST_PP_REPEAT(BOOST_PP_ITERATION(), BOOST_RESULT_OF_STATIC_MEMBERS, _)
+public:
+  typedef decltype(f(BOOST_PP_ENUM_PARAMS(BOOST_PP_ITERATION(),t))) type;
+};
+
+} // namespace detail 
+
+#else // defined(BOOST_HAS_DECLTYPE)
+
 // CWPro8 requires an argument in a function type specialization
 #if BOOST_WORKAROUND(__MWERKS__, BOOST_TESTED_AT(0x3002)) && BOOST_PP_ITERATION() == 0
 # define BOOST_RESULT_OF_ARGS void
@@ -26,6 +66,8 @@ struct result_of<F(BOOST_RESULT_OF_ARGS)>
 
 #undef BOOST_RESULT_OF_ARGS
 
+#endif // defined(BOOST_HAS_DECLTYPE)
+
 #if BOOST_PP_ITERATION() >= 1 
 
 namespace detail {

include/boost/utility/result_of.hpp

@@ -18,6 +18,9 @@
 #include <boost/mpl/has_xxx.hpp>
 #include <boost/mpl/if.hpp>
 #include <boost/mpl/bool.hpp>
+#include <boost/mpl/or.hpp>
+#include <boost/type_traits/is_pointer.hpp>
+#include <boost/type_traits/is_member_function_pointer.hpp>
 
 #ifndef BOOST_RESULT_OF_NUM_ARGS
 #  define BOOST_RESULT_OF_NUM_ARGS 10
@@ -33,6 +36,7 @@ namespace detail {
 BOOST_MPL_HAS_XXX_TRAIT_DEF(result_type)
 
 template<typename F, typename FArgs, bool HasResultType> struct result_of_impl;
+template<typename F> struct result_of_decltype_impl;
 
 template<typename F>
 struct result_of_void_impl

test/result_of_test.cpp

@@ -11,35 +11,101 @@
 #include <boost/static_assert.hpp>
 #include <boost/type_traits/is_same.hpp>
 
-struct int_result_type { typedef int result_type; };
+struct int_result_type
+{
+  typedef int result_type;
+  result_type operator()(float);
+};
 
 struct int_result_of
 {
   template<typename F> struct result { typedef int type; };
+  result<int_result_of(double)>::type operator()(double);
+  result<const int_result_of(double)>::type operator()(double) const;
+  result<int_result_of()>::type operator()();
+  result<volatile int_result_of()>::type operator()() volatile;
 };
 
-struct int_result_type_and_float_result_of
+struct int_result_type_and_float_result_of_and_char_return
 {
   typedef int result_type;
   template<typename F> struct result { typedef float type; };
+  char operator()(char);
 };
 
 template<typename T>
-struct int_result_type_template { typedef int result_type; };
+struct int_result_type_template
+{
+  typedef int result_type;
+  result_type operator()(float);
+};
 
 template<typename T>
 struct int_result_of_template
 {
   template<typename F> struct result;
   template<typename This, typename That> struct result<This(That)> { typedef int type; };
+  typename result<int_result_of_template<T>(double)>::type operator()(double);
+  typename result<const int_result_of_template<T>(double)>::type operator()(double) const;
+  typename result<int_result_of_template<T>(double)>::type operator()();
+  typename result<volatile int_result_of_template<T>(double)>::type operator()() volatile;
 };
 
 template<typename T>
-struct int_result_type_and_float_result_of_template
+struct int_result_type_and_float_result_of_and_char_return_template
 {
   typedef int result_type;
   template<typename F> struct result;
   template<typename This, typename That> struct result<This(That)> { typedef float type; };
+  char operator()(char);
+};
+
+struct result_of_member_function_template
+{
+  template<typename F> struct result;
+
+  template<typename This, typename That> struct result<This(That)> { typedef That type; };
+  template<class T> typename result<result_of_member_function_template(T)>::type operator()(T);
+
+  template<typename This, typename That> struct result<const This(That)> { typedef const That type; };
+  template<class T> typename result<const result_of_member_function_template(T)>::type operator()(T) const;
+
+  template<typename This, typename That> struct result<volatile This(That)> { typedef volatile That type; };
+  template<class T> typename result<volatile result_of_member_function_template(T)>::type operator()(T) volatile;
+
+  template<typename This, typename That> struct result<const volatile This(That)> { typedef const volatile That type; };
+  template<class T> typename result<const volatile result_of_member_function_template(T)>::type operator()(T) const volatile;
+
+  template<typename This, typename That> struct result<This(That &, That)> { typedef That & type; };
+  template<class T> typename result<result_of_member_function_template(T &, T)>::type operator()(T &, T);
+
+  template<typename This, typename That> struct result<This(That const &, That)> { typedef That const & type; };
+  template<class T> typename result<result_of_member_function_template(T const &, T)>::type operator()(T const &, T);
+
+  template<typename This, typename That> struct result<This(That volatile &, That)> { typedef That volatile & type; };
+  template<class T> typename result<result_of_member_function_template(T volatile &, T)>::type operator()(T volatile &, T);
+
+  template<typename This, typename That> struct result<This(That const volatile &, That)> { typedef That const volatile & type; };
+  template<class T> typename result<result_of_member_function_template(T const volatile &, T)>::type operator()(T const volatile &, T);
+};
+
+struct no_result_type_or_result_of
+{
+  int operator()(double);
+  short operator()(double) const;
+  unsigned int operator()();
+  unsigned short operator()() volatile;
+  const unsigned short operator()() const volatile;
+};
+
+template<typename T>
+struct no_result_type_or_result_of_template
+{
+  int operator()(double);
+  short operator()(double) const;
+  unsigned int operator()();
+  unsigned short operator()() volatile;
+  const unsigned short operator()() const volatile;
 };
 
 struct X {};
@@ -60,16 +126,37 @@ int main()
 
   BOOST_STATIC_ASSERT((is_same<result_of<int_result_type(float)>::type, int>::value));
   BOOST_STATIC_ASSERT((is_same<result_of<int_result_of(double)>::type, int>::value));
-  BOOST_STATIC_ASSERT((is_same<result_of<int_result_of(void)>::type, void>::value));
   BOOST_STATIC_ASSERT((is_same<result_of<const int_result_of(double)>::type, int>::value));
-  BOOST_STATIC_ASSERT((is_same<result_of<volatile int_result_of(void)>::type, void>::value));
-  BOOST_STATIC_ASSERT((is_same<result_of<int_result_type_and_float_result_of(char)>::type, int>::value));
   BOOST_STATIC_ASSERT((is_same<result_of<int_result_type_template<void>(float)>::type, int>::value));
   BOOST_STATIC_ASSERT((is_same<result_of<int_result_of_template<void>(double)>::type, int>::value));
-  BOOST_STATIC_ASSERT((is_same<result_of<int_result_of_template<void>(void)>::type, void>::value));
   BOOST_STATIC_ASSERT((is_same<result_of<const int_result_of_template<void>(double)>::type, int>::value));
+
+  // Prior to decltype, result_of could not deduce the return type
+  // nullary function objects unless they exposed a result_type.
+#if defined(BOOST_HAS_DECLTYPE)
+  BOOST_STATIC_ASSERT((is_same<result_of<int_result_of(void)>::type, int>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<volatile int_result_of(void)>::type, int>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<int_result_of_template<void>(void)>::type, int>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<volatile int_result_of_template<void>(void)>::type, int>::value));
+#else
+  BOOST_STATIC_ASSERT((is_same<result_of<int_result_of(void)>::type, void>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<volatile int_result_of(void)>::type, void>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<int_result_of_template<void>(void)>::type, void>::value));
   BOOST_STATIC_ASSERT((is_same<result_of<volatile int_result_of_template<void>(void)>::type, void>::value));
-  BOOST_STATIC_ASSERT((is_same<result_of<int_result_type_and_float_result_of_template<void>(char)>::type, int>::value));
+#endif
+
+  // Prior to decltype, result_of ignored a nested result<> if
+  // result_type was defined. After decltype, result_of deduces the
+  // actual return type of the function object, ignoring both
+  // result<> and result_type.
+#if defined(BOOST_HAS_DECLTYPE)
+  BOOST_STATIC_ASSERT((is_same<result_of<int_result_type_and_float_result_of_and_char_return(char)>::type, char>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<int_result_type_and_float_result_of_and_char_return_template<void>(char)>::type, char>::value));
+#else
+  BOOST_STATIC_ASSERT((is_same<result_of<int_result_type_and_float_result_of_and_char_return(char)>::type, int>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<int_result_type_and_float_result_of_and_char_return_template<void>(char)>::type, int>::value));
+#endif
+
   BOOST_STATIC_ASSERT((is_same<result_of<func_ptr(char, float)>::type, int>::value));
   BOOST_STATIC_ASSERT((is_same<result_of<func_ref(char, float)>::type, int>::value));
   BOOST_STATIC_ASSERT((is_same<result_of<func_ptr_0()>::type, int>::value)); 
@@ -81,5 +168,27 @@ int main()
   BOOST_STATIC_ASSERT((is_same<result_of<mem_func_ptr_0(X)>::type, int>::value)); 
   BOOST_STATIC_ASSERT((is_same<result_of<func_ptr(void)>::type, int>::value));
 
+  BOOST_STATIC_ASSERT((is_same<result_of<result_of_member_function_template(double)>::type, double>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<const result_of_member_function_template(double)>::type, const double>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<volatile result_of_member_function_template(double)>::type, volatile double>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<const volatile result_of_member_function_template(double)>::type, const volatile double>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<result_of_member_function_template(int &, int)>::type, int &>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<result_of_member_function_template(int const &, int)>::type, int const &>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<result_of_member_function_template(int volatile &, int)>::type, int volatile &>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<result_of_member_function_template(int const volatile &, int)>::type, int const volatile &>::value));
+
+#if defined(BOOST_HAS_DECLTYPE)
+  BOOST_STATIC_ASSERT((is_same<result_of<no_result_type_or_result_of(double)>::type, int>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<no_result_type_or_result_of(void)>::type, unsigned int>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<const no_result_type_or_result_of(double)>::type, short>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<volatile no_result_type_or_result_of(void)>::type, unsigned short>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<const volatile no_result_type_or_result_of(void)>::type, const unsigned short>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<no_result_type_or_result_of_template<void>(double)>::type, int>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<no_result_type_or_result_of_template<void>(void)>::type, unsigned int>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<const no_result_type_or_result_of_template<void>(double)>::type, short>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<volatile no_result_type_or_result_of_template<void>(void)>::type, unsigned short>::value));
+  BOOST_STATIC_ASSERT((is_same<result_of<const volatile no_result_type_or_result_of_template<void>(void)>::type, const unsigned short>::value));
+#endif
+
   return 0;
 }

utility.htm

@@ -152,11 +152,13 @@ void f() {
                 ...,t<em>N</em>)</code>. The implementation permits
                 the type <code>F</code> to be a function pointer,
                 function reference, member function pointer, or class
-                type. When <code>F</code> is a class type with a
+                type.</p> <p>If your compiler does not support
-                member type <code>result_type</code>,
+                <code>decltype</code>, then when <code>F</code> is a
+                class type with a member type <code>result_type</code>,
                 <code>result_of&lt;F(T1, T2, ...,
                 T<em>N</em>)&gt;</code> is
-                <code>F::result_type</code>. Otherwise,
+                <code>F::result_type</code>. When <code>F</code>
+                does not contain <code>result_type</code>, 
                 <code>result_of&lt;F(T1, T2, ...,
                 T<em>N</em>)&gt;</code> is <code>F::result&lt;F(T1,
                 T2, ..., T<em>N</em>)&gt;::type</code> when