00001 // Copyright (C) 2007, 2008, 2009 EPITA Research and Development Laboratory (LRDE) 00002 // 00003 // This file is part of Olena. 00004 // 00005 // Olena is free software: you can redistribute it and/or modify it under 00006 // the terms of the GNU General Public License as published by the Free 00007 // Software Foundation, version 2 of the License. 00008 // 00009 // Olena is distributed in the hope that it will be useful, 00010 // but WITHOUT ANY WARRANTY; without even the implied warranty of 00011 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 00012 // General Public License for more details. 00013 // 00014 // You should have received a copy of the GNU General Public License 00015 // along with Olena. If not, see <http://www.gnu.org/licenses/>. 00016 // 00017 // As a special exception, you may use this file as part of a free 00018 // software project without restriction. Specifically, if other files 00019 // instantiate templates or use macros or inline functions from this 00020 // file, or you compile this file and link it with other files to produce 00021 // an executable, this file does not by itself cause the resulting 00022 // executable to be covered by the GNU General Public License. This 00023 // exception does not however invalidate any other reasons why the 00024 // executable file might be covered by the GNU General Public License. 00025 00026 #ifndef MLN_CORE_CATEGORY_HH 00027 # define MLN_CORE_CATEGORY_HH 00028 00032 00033 # include <mln/metal/equal.hh> 00034 00035 00036 00037 namespace mln 00038 { 00039 00040 // FIXME: Doc! 00041 00042 00043 template <typename E> 00044 struct Unknown; 00045 00046 00047 template <> 00048 struct Unknown<void> 00049 { 00050 typedef Unknown<void> super; 00051 // Unknown is used to terminate the meta-program that solves a 00052 // call to a trait. This meta-program can browse several branches 00053 // at the same time---if the trait takes 2 types as arguments, the 00054 // program runs over the trellis formed by the "couples of 00055 // categories"--- and when the end of one branch is reached, we do 00056 // not want the program to end; so it continues on that branch 00057 // with the no-op "jump to the super type of Unknown"! 00058 }; 00059 00060 00061 template <typename T> 00062 struct category 00063 { 00064 typedef typename T::category ret; // FIXME: if found or Unknown<void> => write a meta-program... 00065 }; 00066 00067 template <typename T> 00068 struct category< const T > 00069 { 00070 typedef typename category<T>::ret ret; 00071 }; 00072 00073 00074 00075 // Utility meta-function: from a category and a type, get the super category. 00076 00077 namespace internal 00078 { 00079 00080 // The code above could be merged into a couple of structures. 00081 // Yet g++-2.95 needs help so we first decompose Category<S> 00082 // into (Category, S) then we solve. 00083 00084 template < template <class> class Category, typename S, typename T > 00085 struct helper_super_category_solve_ 00086 : 00087 private metal::equal< typename Category<void>::super, void* >::check_t 00088 { 00089 // New case. 00090 typedef S ret; 00091 }; 00092 00093 template < template <class> class Category, typename T > 00094 struct helper_super_category_solve_< Category, void, T > 00095 { 00096 typedef typename Category<void>::super ret; // One super category: keep it. 00097 }; 00098 00099 template < typename Category, typename T > 00100 struct helper_super_category_; 00101 00102 template < template <class> class Category, typename S, typename T > 00103 struct helper_super_category_< Category<S>, T > : helper_super_category_solve_< Category, S, T > 00104 { 00105 }; 00106 00107 00108 00109 // For bwd in-compatibility. 00110 template < template <class> class Category, typename T > 00111 struct helper_super_category_< Category<void*>, T >; 00112 00113 00114 template < typename Category, typename T > 00115 struct super_category_ // Entry. 00116 { 00117 typedef typename helper_super_category_< Category, T >::ret ret; 00118 }; 00119 00120 } // end of namespace mln::internal 00121 00122 00123 } // end of namespace mln 00124 00125 00126 #endif // ! MLN_CORE_CATEGORY_HH