4 // Fraunhofer Institut fuer offene Kommunikationssysteme (FOKUS)
5 // Kompetenzzentrum fuer Satelitenkommunikation (SatCom)
6 // Stefan Bund <g0dil@berlios.de>
8 // This program is free software; you can redistribute it and/or modify
9 // it under the terms of the GNU General Public License as published by
10 // the Free Software Foundation; either version 2 of the License, or
11 // (at your option) any later version.
13 // This program is distributed in the hope that it will be useful,
14 // but WITHOUT ANY WARRANTY; without even the implied warranty of
15 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 // GNU General Public License for more details.
18 // You should have received a copy of the GNU General Public License
19 // along with this program; if not, write to the
20 // Free Software Foundation, Inc.,
21 // 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
24 \brief mpl public header */
30 #include "../config.hh"
34 ///////////////////////////////hh.p////////////////////////////////////////
39 /** \defgroup senfmpl Template meta programming helpers
42 /** \brief Marker class for empty default values etc.
44 This is like Boosts \c boost::mpl::na just an empty class used as template default argument
45 to mark missing arguments
47 \note Don't use this as an empty base class. We may add some informative members to this.
51 /** \brief Return-value type used to implement overload selection
53 The senf::mpl::rv type is used together with \ref SENF_MPL_RV() to select template
54 specializations based on a set of overloads:
57 template <unsigned _> struct select {};
62 static bool const has_int_value = true;
66 senf::mpl::rv<0> select_(int, senf::mpl::take_int<T::value> * = 0);
71 static bool const has_int_value = false;
75 senf::mpl::rv<1> select_(...);
78 struct choice : public select<SENF_MPL_RV( select_<T>(0) )> {};
80 struct A { static const int value = 0; };
83 choice<A> a; a.frobble();
84 choice<B> b; b.dazzle();
87 The selection is always based on two components: A selector class specialized for each of
88 the possible choices and an overloaded function (only signatures, no implementation needed)
89 to provide the conditions.
91 When instantiatinv <tt>choice<T></tt>, we forward \a T to the <tt>select_</tt> set of
92 overloads. Because of <a href="http://en.wikipedia.org/wiki/SFINAE">SFINAE</a>, the overload
93 set will only contain those instantiations, for which template expansion does not fail.
95 So, if \a T has an integer \c value member, both \c select_ overloads are ok and the call
96 <tt>select_<T>(0)</tt> will choose the first (case 0) variant, since the argument \c 0 is
97 better matched by \c int than by <tt>...</tt>.
99 However, if \a T does not have an integer \c value member, expansion for the first overload
100 fails and the overload set only contains the second case.
102 \ref SENF_MPL_RV() internally uses \c sizeof to find out, \e which overload was selected
103 and returns the senf::mpl::rv-argument of that overloads return type. For this to work, the
104 \c select_ functions need not be implemented since no code is generated and \c select_ is
107 This number is than forwarded as template argument to \c select which is specialized for
108 each case. Therefore, <tt>choice\<A\></tt> has a \c frobble() member whereas
109 <tt>choice\<B\></tt> has a \c dazzle() member.
111 \see \ref SENF_MPL_RV
114 template <unsigned n>
116 char _[SENF_MPL_RV_ALIGNMENT][n+1];
119 /** \brief Get return value of overload selector
121 Used together with senf::mpl::rv to implement overload selection.
123 \see \ref senf::mpl::rv
127 # define SENF_MPL_RV(expr) (sizeof(expr)/SENF_MPL_RV_ALIGNMENT-1)
129 /** \brief Take an arbitrary unsigned integer template argument
131 Used together with <a href="http://en.wikipedia.org/wiki/SFINAE">SFINAE</a>: The expression
132 <tt>take_uint<</tt> \a expr <tt>></tt> is only valid if \a expr is valid and returns a value
133 convertible to an unsigned integer.
137 template <unsigned long _> struct take_uint {};
139 /** \brief Take an arbitrary integer template argument
141 Used together with <a href="http://en.wikipedia.org/wiki/SFINAE">SFINAE</a>: The expression
142 <tt>take_int<</tt> \a expr <tt>></tt> is only valid if \a expr is valid and returns a value
143 convertible to an integer.
147 template <long _> struct take_int {};
149 /** \brief Take an arbitrary type template argument
151 Used together with <a href="http://en.wikipedia.org/wiki/SFINAE">SFINAE</a>: The expression
152 <tt>take_class<</tt> \a expr <tt>></tt> is only valid if \a expr is valid and is a type.
156 template <class _> struct take_class {};
158 /** \brief Define MPL slot
160 The slot macros \ref SENF_MPL_SLOT_DEF(), \ref SENF_MPL_SLOT_SET() and \ref
161 SENF_MPL_SLOT_GET() provide a facility to get the last unsigned integer value assigned to
162 the slot before the current point in the current class.
166 // Define SLOT slot named 'accum' initialized to 0
167 SENF_MPL_SLOT_DEF(accum, 0);
170 SENF_MPL_SLOT_SET(accum, SENF_MPL_SLOT_GET(accum) + 2);
172 // Multiply 'accum' by 3
173 SENF_MPL_SLOT_SET(accum, SENF_MPL_SLOT_GET(accum) * 3);
175 // Define the result as a constant expression. result is now 6
176 static unsigned result = SENF_MPL_SLOT_GET(accum);
179 Of course, it does not make sense to use these macros for simple arithmetic as in the
180 example. The SENF_MPL_SLOT macros allow to define macros which pass information from one
181 macro invocation to the next.
183 \implementation The implementation is based on __LINE__: We check backwards for a value
184 defined on a previous line. The check is limited to 80 lines backwards.
189 # define SENF_MPL_SLOT_DEF(name,value) \
191 static senf::mpl::rv<0> _SENF_MPL_SLOT_ ## name (_); \
192 SENF_MPL_SLOT_SET(name,value)
194 /** \brief Define MPL slot initialized to 0
196 This is like \ref SENF_MPL_SLOT_DEF() but initializes the slot to the fixed value 0. The
197 advantage over \ref SENF_MPL_SLOT_DEF() is, that this macro may be called from an include
198 file whereas all the other \\c SENF_MPL_SLOT_ macros must always be called from the relevant
201 # define SENF_MPL_SLOT_DEF_ZERO(name) \
203 static senf::mpl::rv<0> _SENF_MPL_SLOT_ ## name (_);
205 /** \brief Set MPL slot
206 \see \ref SENF_MPL_SLOT_DEF()
210 # define SENF_MPL_SLOT_SET(name,value) \
211 static senf::mpl::rv<unsigned(value)+1> \
212 _SENF_MPL_SLOT_ ## name (senf::mpl::take_int<__LINE__>)
214 /** \brief Get current MPL slot value
215 \see \ref SENF_MPL_SLOT_DEF()
219 # define SENF_MPL_SLOT_GET(name) \
220 SENF_MPL_SLOT_I_GET(name)
224 ///////////////////////////////hh.e////////////////////////////////////////
234 // comment-column: 40
235 // c-file-style: "senf"
236 // indent-tabs-mode: nil
237 // ispell-local-dictionary: "american"
238 // compile-command: "scons -u test"