[Boost-commit] svn:boost r77025 - in trunk/boost/functional: . overloaded_function overloaded_function/detail

Subject: [Boost-commit] svn:boost r77025 - in trunk/boost/functional: . overloaded_function overloaded_function/detail
From: lorcaminiti_at_[hidden]
Date: 2012-02-14 19:42:57

Author: lcaminiti
Date: 2012-02-14 19:42:56 EST (Tue, 14 Feb 2012)
New Revision: 77025
URL: http://svn.boost.org/trac/boost/changeset/77025

Log:
Added Functional/OverloadedFunction source files.
Added:
   trunk/boost/functional/overloaded_function/
   trunk/boost/functional/overloaded_function.hpp   (contents, props changed)
   trunk/boost/functional/overloaded_function/config.hpp   (contents, props changed)
   trunk/boost/functional/overloaded_function/detail/
   trunk/boost/functional/overloaded_function/detail/base.hpp   (contents, props changed)
   trunk/boost/functional/overloaded_function/detail/function_type.hpp   (contents, props changed)

Added: trunk/boost/functional/overloaded_function.hpp
==============================================================================
--- (empty file)
+++ trunk/boost/functional/overloaded_function.hpp	2012-02-14 19:42:56 EST (Tue, 14 Feb 2012)
@@ -0,0 +1,293 @@
+
+// Copyright (C) 2009-2012 Lorenzo Caminiti
+// Distributed under the Boost Software License, Version 1.0
+// (see accompanying file LICENSE_1_0.txt or a copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+// Home at http://www.boost.org/libs/functional/overloaded_function
+
+#ifndef DOXYGEN // Doxygen documentation only.
+
+#if !BOOST_PP_IS_ITERATING
+#   ifndef BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_HPP_
+#       define BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_HPP_
+
+#       include <boost/functional/overloaded_function/detail/base.hpp>
+#       include <boost/functional/overloaded_function/detail/function_type.hpp>
+#       include <boost/functional/overloaded_function/config.hpp>
+#       include <boost/preprocessor/iteration/iterate.hpp>
+#       include <boost/preprocessor/repetition/enum.hpp>
+#       include <boost/preprocessor/repetition/repeat.hpp>
+#       include <boost/preprocessor/control/expr_iif.hpp>
+#       include <boost/preprocessor/control/expr_if.hpp>
+#       include <boost/preprocessor/comparison/greater.hpp>
+#       include <boost/preprocessor/comparison/less.hpp>
+#       include <boost/preprocessor/cat.hpp>
+#       include <boost/preprocessor/arithmetic/add.hpp>
+#       include <boost/preprocessor/tuple/eat.hpp>
+#       include <boost/preprocessor/logical/and.hpp>
+#       include <boost/preprocessor/logical/not.hpp>
+#       include <boost/preprocessor/facilities/expand.hpp>
+
+#define BOOST_FUNCTIONAL_f_type(z, n, unused) \
+    BOOST_PP_CAT(F, n)
+
+#define BOOST_FUNCTIONAL_f_arg(z, n, unused) \
+    BOOST_PP_CAT(f, n)
+
+#define BOOST_FUNCTIONAL_f_tparam(z, n, unused) \
+    typename BOOST_FUNCTIONAL_f_type(z, n, ~) \
+
+#define BOOST_FUNCTIONAL_f_tparam_dflt(z, n, is_tspec) \
+    BOOST_FUNCTIONAL_f_tparam(z, n, ~) \
+    /* overload requires at least 2 functors so F0 and F1 not optional */ \
+    BOOST_PP_EXPR_IIF(BOOST_PP_AND(BOOST_PP_NOT(is_tspec), \
+            BOOST_PP_GREATER(n, 1)), \
+        = void \
+    )
+
+#define BOOST_FUNCTIONAL_f_arg_decl(z, n, unused) \
+    BOOST_FUNCTIONAL_f_type(z, n, ~) /* no qualifier to deduce tparam */ \
+    BOOST_FUNCTIONAL_f_arg(z, n, ~)
+
+#define BOOST_FUNCTIONAL_g_type(z, n, unused) \
+    BOOST_PP_CAT(G, n)
+
+#define BOOST_FUNCTIONAL_g_arg(z, n, unused) \
+    BOOST_PP_CAT(g, n)
+
+#define BOOST_FUNCTIONAL_g_tparam(z, n, unused) \
+    typename BOOST_FUNCTIONAL_g_type(z, n, ~)
+
+#define BOOST_FUNCTIONAL_g_arg_decl(z, n, unused) \
+    BOOST_FUNCTIONAL_g_type(z, n, ~) /* no qualifier to deduce tparam */ \
+    BOOST_FUNCTIONAL_g_arg(z, n, ~)
+
+#define BOOST_FUNCTIONAL_base(z, n, unused) \
+    ::boost::overloaded_function_detail::base< \
+        BOOST_FUNCTIONAL_f_type(z, n, ~) \
+    >
+
+#define BOOST_FUNCTIONAL_inherit(z, n, unused) \
+    public BOOST_FUNCTIONAL_base(z, n, ~)
+
+#define BOOST_FUNCTIONAL_base_init(z, n, unused) \
+    BOOST_FUNCTIONAL_base(z, n, ~)(BOOST_FUNCTIONAL_g_arg(z, n, ~))
+
+#define BOOST_FUNCTIONAL_using_operator_call(z, n, unused) \
+    using BOOST_FUNCTIONAL_base(z, n, ~)::operator();
+
+#define BOOST_FUNCTIONAL_function_type(z, n, unused) \
+    typename ::boost::overloaded_function_detail::function_type< \
+        BOOST_FUNCTIONAL_f_type(z, n, ~) \
+    >::type
+
+namespace boost {
+
+// Iterate within namespace.
+#       define BOOST_PP_ITERATION_PARAMS_1 \
+                (3, (0, BOOST_PP_SUB( /*at least 2 func to overload 2, 3, ...*/\
+                 BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_OVERLOAD_MAX, 2), \
+                "boost/functional/overloaded_function.hpp"))
+#       include BOOST_PP_ITERATE() // Iterate over function arity.
+
+} // namespace
+
+#undef BOOST_FUNCTIONAL_f_type
+#undef BOOST_FUNCTIONAL_f_arg
+#undef BOOST_FUNCTIONAL_f_tparam
+#undef BOOST_FUNCTIONAL_f_arg_decl
+#undef BOOST_FUNCTIONAL_f_tparam_dflt
+#undef BOOST_FUNCTIONAL_g_type
+#undef BOOST_FUNCTIONAL_g_arg
+#undef BOOST_FUNCTIONAL_g_tparam
+#undef BOOST_FUNCTIONAL_g_arg_decl
+#undef BOOST_FUNCTIONAL_base
+#undef BOOST_FUNCTIONAL_inherit
+#undef BOOST_FUNCTIONAL_base_init
+#undef BOOST_FUNCTIONAL_using_operator_call
+#undef BOOST_FUNCTIONAL_function_type
+
+#   endif // #include guard
+
+#elif BOOST_PP_ITERATION_DEPTH() == 1
+#   define BOOST_FUNCTIONAL_overloads \
+        /* iterate as OVERLOADS, OVERLOADS-1, OVERLOADS-2, ... */ \
+        BOOST_PP_SUB(BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_OVERLOAD_MAX, \
+                BOOST_PP_FRAME_ITERATION(1))
+#   define BOOST_FUNCTIONAL_is_tspec \
+        /* if template specialization */ \
+        BOOST_PP_LESS(BOOST_FUNCTIONAL_overloads, \
+                BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_OVERLOAD_MAX)
+
+template<
+    BOOST_PP_ENUM(BOOST_FUNCTIONAL_overloads, BOOST_FUNCTIONAL_f_tparam_dflt,
+            BOOST_FUNCTIONAL_is_tspec)
+>
+class overloaded_function
+    // Template specialization.
+    BOOST_PP_EXPR_IIF(BOOST_PP_EXPAND(BOOST_FUNCTIONAL_is_tspec), <)
+    BOOST_PP_IIF(BOOST_FUNCTIONAL_is_tspec,
+        BOOST_PP_ENUM
+    ,
+        BOOST_PP_TUPLE_EAT(3)
+    )(BOOST_FUNCTIONAL_overloads, BOOST_FUNCTIONAL_f_type, ~)
+    BOOST_PP_EXPR_IIF(BOOST_PP_EXPAND(BOOST_FUNCTIONAL_is_tspec), >)
+    // Bases (overloads >= 2 so always at least 2 bases).
+    : BOOST_PP_ENUM(BOOST_FUNCTIONAL_overloads,
+            BOOST_FUNCTIONAL_inherit, ~)
+{
+public:
+    template<
+        BOOST_PP_ENUM(BOOST_FUNCTIONAL_overloads, BOOST_FUNCTIONAL_g_tparam, ~)
+    > /* implicit */ inline overloaded_function(
+            BOOST_PP_ENUM(BOOST_FUNCTIONAL_overloads,
+                    BOOST_FUNCTIONAL_g_arg_decl, ~))
+            // Overloads >= 2 so always at least 2 bases to initialize.
+            : BOOST_PP_ENUM(BOOST_FUNCTIONAL_overloads,
+                    BOOST_FUNCTIONAL_base_init, ~)
+    {}
+
+    BOOST_PP_REPEAT(BOOST_FUNCTIONAL_overloads, 
+            BOOST_FUNCTIONAL_using_operator_call, ~)
+};
+
+template<
+    BOOST_PP_ENUM(BOOST_FUNCTIONAL_overloads, BOOST_FUNCTIONAL_f_tparam, ~)
+>
+overloaded_function<
+    BOOST_PP_ENUM(BOOST_FUNCTIONAL_overloads, BOOST_FUNCTIONAL_function_type, ~)
+> make_overloaded_function(
+    BOOST_PP_ENUM(BOOST_FUNCTIONAL_overloads, BOOST_FUNCTIONAL_f_arg_decl, ~)
+) {
+    return overloaded_function<
+        BOOST_PP_ENUM(BOOST_FUNCTIONAL_overloads,
+                BOOST_FUNCTIONAL_function_type, ~)
+    >(BOOST_PP_ENUM(BOOST_FUNCTIONAL_overloads, BOOST_FUNCTIONAL_f_arg, ~));
+}
+
+#   undef BOOST_FUNCTIONAL_overloads
+#   undef BOOST_FUNCTIONAL_is_tspec
+#endif // iteration
+
+// DOCUMENTATION //
+
+#else // DOXYGEN
+
+/** @file
+@brief Overload distinct function pointers, function references, and function
+objects into a single function object.
+*/
+
+namespace boost {
+
+/**
+@brief Function object to overload functions with distinct signatures.
+
+This function object aggregates together calls to functions of all the
+specified function types <c>F1</c>, <c>F2</c>, etc.
+The specified function types must have distinct parameters from one another and
+they must be in the following format (which is the Boost.Function preferred
+syntax):
+@code
+    result_type (argument1_type, argumgnet2_type, ...)
+@endcode
+
+In some cases, the @RefFunc{make_overloaded_function} function template can be
+useful to construct the overloaded function object without explicitly
+specifying the function types.
+
+The maximum number of functions to overload is given by the
+@RefMacro{BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_OVERLOAD_MAX}
+configuration macro.
+The maximum number of function parameters for each of the specified function
+types is given by the
+@RefMacro{BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_ARITY_MAX}
+configuration macro.
+
+@See
+    @RefSect{Tutorial} section,
+    @RefFunc{make_overloaded_function},
+    @RefMacro{BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_OVERLOAD_MAX},
+    @RefMacro{BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_ARITY_MAX},
+    Boost.Function.
+*/
+template<typename F1, typename F2, ...>
+class overloaded_function {
+public:
+    /**
+    @brief Construct the overloaded function object.
+
+    Any function pointer, function reference, and monomorphic function object
+    that can be converted to a <c>boost::function</c> function object can be
+    specified as parameter.
+    */
+    overloaded_function(const boost::function<F1>&,
+            const boost::function<F2>&, ...);
+
+    /**
+    @brief Call operator matching the signature of the function type specified
+    as 1st template parameter.
+
+    This will in turn invoke the call operator of the 1st function passed to
+    the constructor.
+    */
+    typename boost::function_traits<F1>::result_type operator()(
+            typename boost::function_traits<F1>::arg1_type,
+            typename boost::function_traits<F1>::arg2_type,
+            ...) const;
+
+    /**
+    @brief Call operator matching the signature of the function type specified
+    as 2nd template parameter.
+
+    This will in turn invoke the call operator of the 2nd function passed to
+    the constructor.
+
+    @Note Similar call operators are present for all specified function types
+    <c>F1</c>, <c>F2</c>, etc (even if not exhaustively listed by this
+    documentation).
+    */
+    typename boost::function_traits<F2>::result_type operator()(
+            typename boost::function_traits<F2>::arg1_type,
+            typename boost::function_traits<F2>::arg2_type,
+            ...) const;
+};
+
+/**
+@brief Make an overloaded function object without explicitly specifying the
+function types.
+
+This function template creates and returns an @RefClass{overloaded_function}
+function object that overloads all the specified functions <c>f1</c>,
+<c>f2</c>, etc.
+
+The function types are internally determined from the template parameter types
+so they do not need to be explicitly specified.
+Therefore, this function template usually has a more concise syntax when
+compared with @RefClass{overloaded_function}.
+This is especially useful when the explicit type of the returned
+@RefClass{overloaded_function} does not need to be known (e.g., when used with Boost.Typeof's <c>BOOST_AUTO</c> (or C++11 <c>auto</c>) or when the overloaded
+function object is handled using a function template parameter, see the
+@RefSect{Tutorial} section).
+
+The maximum number of functions to overload is given by the
+@RefMacro{BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_OVERLOAD_MAX}
+configuration macro.
+
+@Note In this documentation, <c>__function_type__</c> is a placeholder for a
+symbol that is specific to implementation of this library.
+
+@See
+    @RefSect{Tutorial} section,
+    @RefClass{overloaded_function},
+    @RefMacro{BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_OVERLOAD_MAX}.
+*/
+template<typename F1, typename F2, ...>
+overloaded_function<
+    __function_type__<F1>, __function_type__<F2>, ...
+> make_overloaded_function(F1 f1, F2 f2, ...);
+
+} // namespace
+
+#endif // DOXYGEN
+

Added: trunk/boost/functional/overloaded_function/config.hpp
==============================================================================
--- (empty file)
+++ trunk/boost/functional/overloaded_function/config.hpp	2012-02-14 19:42:56 EST (Tue, 14 Feb 2012)
@@ -0,0 +1,52 @@
+
+// Copyright (C) 2009-2012 Lorenzo Caminiti
+// Distributed under the Boost Software License, Version 1.0
+// (see accompanying file LICENSE_1_0.txt or a copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+// Home at http://www.boost.org/libs/functional/overloaded_function
+
+#ifndef BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_HPP_
+#define BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_HPP_
+
+/** @file
+@brief Change the compile-time configuration of this library.
+*/
+
+/**
+@brief Specify the maximum number of arguments of the functions being
+overloaded.
+
+If this macro is left undefined by the user, it has a default value of 5
+(increasing this number might increase compilation time).
+When specified by the user, this macro must be a non-negative integer number.
+
+@See
+    @RefSectId{Getting_Started, Getting Started},
+    @RefClass{boost::overloaded_function}.
+*/
+#ifndef BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_ARITY_MAX 
+#define BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_ARITY_MAX 5
+#endif
+
+/**
+@brief Specify the maximum number of functions that can be overloaded.
+
+If this macro is left undefined by the user, it has a default value of 5
+(increasing this number might increase compilation time).
+When defined by the user, this macro must be an integer number greater or
+equal than 2 (because at least two distinct functions need to be specified in
+order to define an overload).
+
+@See
+    @RefSectId{Getting_Started, Getting Started},
+    @RefClass{boost::overloaded_function}.
+*/
+#ifndef BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_OVERLOAD_MAX
+#define BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_OVERLOAD_MAX 5
+#endif
+#if BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_OVERLOAD_MAX < 2
+#error "BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_OVERLOAD_MAX must be >= 2"
+#endif
+
+#endif // #include guard
+

Added: trunk/boost/functional/overloaded_function/detail/base.hpp
==============================================================================
--- (empty file)
+++ trunk/boost/functional/overloaded_function/detail/base.hpp	2012-02-14 19:42:56 EST (Tue, 14 Feb 2012)
@@ -0,0 +1,85 @@
+
+// Copyright (C) 2009-2012 Lorenzo Caminiti
+// Distributed under the Boost Software License, Version 1.0
+// (see accompanying file LICENSE_1_0.txt or a copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+// Home at http://www.boost.org/libs/functional/overloaded_function
+
+#if !BOOST_PP_IS_ITERATING
+#   ifndef BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_DETAIL_BASE_HPP_
+#       define BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_DETAIL_BASE_HPP_
+
+#       include <boost/functional/overloaded_function/config.hpp>
+#       include <boost/function.hpp>
+#       include <boost/preprocessor/iteration/iterate.hpp>
+#       include <boost/preprocessor/repetition/enum.hpp>
+#       include <boost/preprocessor/cat.hpp>
+#       include <boost/preprocessor/comma_if.hpp>
+
+#define BOOST_FUNCTIONAL_DETAIL_arg_type(z, n, unused) \
+    BOOST_PP_CAT(A, n)
+
+#define BOOST_FUNCTIONAL_DETAIL_arg_name(z, n, unused) \
+    BOOST_PP_CAT(a, n)
+
+#define BOOST_FUNCTIONAL_DETAIL_arg_tparam(z, n, unused) \
+    typename BOOST_FUNCTIONAL_DETAIL_arg_type(z, n, unused)
+
+#define BOOST_FUNCTIONAL_DETAIL_arg(z, n, unused) \
+    BOOST_FUNCTIONAL_DETAIL_arg_type(z, n, unused) \
+    BOOST_FUNCTIONAL_DETAIL_arg_name(z, n, unused)
+
+#define BOOST_FUNCTIONAL_DETAIL_f \
+    R (BOOST_PP_ENUM(BOOST_FUNCTIONAL_DETAIL_arity, \
+            BOOST_FUNCTIONAL_DETAIL_arg_type, ~))
+
+namespace boost { namespace overloaded_function_detail {
+
+template<typename F>
+class base {}; // Empty template cannot be used directly (only its spec).
+
+#       define BOOST_PP_ITERATION_PARAMS_1 \
+                (3, (0, BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_CONFIG_ARITY_MAX, \
+                "boost/functional/overloaded_function/detail/base.hpp"))
+#       include BOOST_PP_ITERATE() // Iterate over funciton arity.
+
+} } // namespace
+
+#undef BOOST_FUNCTIONAL_DETAIL_arg_type
+#undef BOOST_FUNCTIONAL_DETAIL_arg_name
+#undef BOOST_FUNCTIONAL_DETAIL_arg_tparam
+#undef BOOST_FUNCTIONAL_DETAIL_arg
+#undef BOOST_FUNCTIONAL_DETAIL_f
+
+#   endif // #include guard
+
+#elif BOOST_PP_ITERATION_DEPTH() == 1
+#   define BOOST_FUNCTIONAL_DETAIL_arity BOOST_PP_FRAME_ITERATION(1)
+
+template<
+    typename R
+    BOOST_PP_COMMA_IF(BOOST_FUNCTIONAL_DETAIL_arity)
+    BOOST_PP_ENUM(BOOST_FUNCTIONAL_DETAIL_arity,
+            BOOST_FUNCTIONAL_DETAIL_arg_tparam, ~)
+>
+class base< BOOST_FUNCTIONAL_DETAIL_f > {
+public:
+    /* implicit */ inline base(
+            // This requires specified type to be implicitly convertible to
+            // a boost::function<> functor.
+            boost::function< BOOST_FUNCTIONAL_DETAIL_f > const& f): f_(f)
+    {}
+
+    inline R operator()(BOOST_PP_ENUM(BOOST_FUNCTIONAL_DETAIL_arity,
+            BOOST_FUNCTIONAL_DETAIL_arg, ~)) const {
+        return f_(BOOST_PP_ENUM(BOOST_FUNCTIONAL_DETAIL_arity,
+                BOOST_FUNCTIONAL_DETAIL_arg_name, ~));
+    }
+
+private:
+    boost::function< BOOST_FUNCTIONAL_DETAIL_f > const f_;
+};
+
+#   undef BOOST_FUNCTIONAL_DETAIL_arity
+#endif // iteration
+

Added: trunk/boost/functional/overloaded_function/detail/function_type.hpp
==============================================================================
--- (empty file)
+++ trunk/boost/functional/overloaded_function/detail/function_type.hpp	2012-02-14 19:42:56 EST (Tue, 14 Feb 2012)
@@ -0,0 +1,73 @@
+
+// Copyright (C) 2009-2012 Lorenzo Caminiti
+// Distributed under the Boost Software License, Version 1.0
+// (see accompanying file LICENSE_1_0.txt or a copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+// Home at http://www.boost.org/libs/functional/overloaded_function
+
+#ifndef BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_DETAIL_FUNCTION_TYPE_HPP_
+#define BOOST_FUNCTIONAL_OVERLOADED_FUNCTION_DETAIL_FUNCTION_TYPE_HPP_
+
+#include <boost/function_types/is_function.hpp>
+#include <boost/function_types/is_function_pointer.hpp>
+#include <boost/function_types/is_function_reference.hpp>
+#include <boost/function_types/function_type.hpp>
+#include <boost/function_types/parameter_types.hpp>
+#include <boost/function_types/result_type.hpp>
+#include <boost/type_traits/remove_pointer.hpp>
+#include <boost/type_traits/remove_reference.hpp>
+#include <boost/mpl/if.hpp>
+#include <boost/mpl/identity.hpp>
+#include <boost/mpl/pop_front.hpp>
+#include <boost/mpl/push_front.hpp>
+#include <boost/typeof/typeof.hpp>
+
+namespace boost { namespace overloaded_function_detail {
+
+// Requires: F is a monomorphic functor (i.e., has non-template `operator()`).
+// Returns: F's function type `result_type (arg1_type, arg2_type, ...)`.
+// It does not assume F typedef result_type, arg1_type, ... but needs typeof.
+template<typename F>
+class functor_type {
+    typedef BOOST_TYPEOF_TPL(&(F::operator())) call_ptr;
+public:
+    typedef
+        typename boost::function_types::function_type<
+            typename boost::mpl::push_front<
+                  typename boost::mpl::pop_front< // Remove functor type (1st).
+                    typename boost::function_types::parameter_types<
+                            call_ptr>::type
+                  >::type
+                , typename boost::function_types::result_type<call_ptr>::type
+            >::type
+        >::type
+    type;
+};
+
+// Requires: F is a function type, pointer, reference, or monomorphic functor.
+// Returns: F's function type `result_type (arg1_type, arg2_type, ...)`.
+template<typename F>
+struct function_type {
+    typedef
+        typename boost::mpl::if_<boost::function_types::is_function<F>,
+            boost::mpl::identity<F>
+        ,
+            typename boost::mpl::if_<boost::function_types::
+                    is_function_pointer<F>,
+                boost::remove_pointer<F>
+            ,
+                typename boost::mpl::if_<boost::function_types::
+                        is_function_reference<F>,
+                    boost::remove_reference<F>
+                , // Requires, it's a functor.
+                    functor_type<F>
+                >::type
+            >::type
+        >::type
+    ::type type;
+};
+
+} } // namespace
+
+#endif // #include guard
+