Generating Switch Statements in C++

genswitch.cpp

/* Copyright (C) 2012 Christopher Schwaab
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
#include <stdio.h>
#include <switch.hpp>

enum { ADD = 0, SUB = 1, MUL = 2, DIV = 3, MOD = 4 };

template <int Operation>
struct interpreter {
    static inline int run(const int x, const int y);
};

template <> struct interpreter<ADD> {
    static const char *name() { return "ADD"; }
    static inline int run(const int x, const int y)
    { return x + y; }
};

template <> struct interpreter<SUB> {
    static const char *name() { return "SUB"; }
    static inline int run(const int x, const int y)
    { return x - y; }
};

template <> struct interpreter<MUL> {
    static const char *name() { return "MUL"; }
    static inline int run(const int x, const int y)
    { return x * y; }
};

template <> struct interpreter<DIV> {
    static const char *name() { return "DIV"; }
    static inline int run(const int x, const int y)
    { return x / y; }
};

template <> struct interpreter<MOD> {
    static const char *name() { return "MOD"; }
    static inline int run(const int x, const int y)
    { return x % y; }
};

template <int Operation>
struct operation_table {
    static always_inline int value(const bool printResult, const int x, const int y) {
        const int r = interpreter<Operation>::run(x, y);
        if (printResult) printf("operation_table<%s>::run(%i, %i) = %i\n",
                                 interpreter<Operation>::name(), x, y, r);
        return r;
    }
};

int main() {
    int(*operations[])(const bool,const int,const int) = {
        operation_table<ADD>::value, operation_table<SUB>::value,
        operation_table<MUL>::value, operation_table<DIV>::value,
        operation_table<MOD>::value
    };

    bool printResult = true;
    int op,x,y;

    printf("op,x,y: ");
    scanf("%i,%i,%i", &op, &x, &y);

    metalevel::switch_table<ADD, MOD, operation_table>::run<int>(op,printResult,
                                                                 x,y);
    operations[op](printResult,x,y);

    return 0;
}

switch.hpp

/* Copyright (C) 2012 Christopher Schwaab
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
#ifndef _metalevel_switch_h_
#define _metalevel_switch_h_

#include <boost/mpl/at.hpp>
#include <boost/mpl/if.hpp>
#include <boost/mpl/list.hpp>
#include <boost/mpl/pair.hpp>
#include <boost/mpl/push_front.hpp>
#include <boost/mpl/size.hpp>

#include <boost/preprocessor/iterate.hpp>
#include <boost/preprocessor/repetition/enum_params.hpp>
#include <boost/preprocessor/repetition/enum_binary_params.hpp>
#include <boost/preprocessor/repetition/repeat.hpp>

#ifdef __GNUC__
#  define always_inline __attribute__((always_inline))
#elif defined(_MSC_VER)
#  define always_inline __forceinline
#else
#  define always_inline inline
#endif

#ifndef METALEVEL_MAX_CHOICE_ARGS
#  define METALEVEL_MAX_CHOICE_ARGS 20
#endif

#ifndef METALEVEL_MAX_SWITCH_SIZE
#  define METALEVEL_MAX_SWITCH_SIZE 20
#endif

namespace metalevel {

namespace aux {
    template <int NumberOfCases, typename Xs>
    struct switch_impl;
#   define BOOST_PP_ITERATION_LIMITS (0, METALEVEL_MAX_SWITCH_SIZE)
#   define BOOST_PP_FILENAME_1 <switch_impl.hpp>
#   include BOOST_PP_ITERATE()

    template <int Counter, int N, template <int> class Table>
    struct tabulate
      : boost::mpl::push_front<
          tabulate<Counter-1, N-1, Table>,
          boost::mpl::pair<boost::mpl::int_<N>, Table<N> >
        >::type {};

    template <int N, template <int> class Table>
    struct tabulate<0, N, Table>
      : boost::mpl::list<
          boost::mpl::pair<boost::mpl::int_<N>, Table<N> >
        > {};
} // namespace aux

template <typename Xs>
struct switch_
  : aux::switch_impl<boost::mpl::size<Xs>::type::value - 1, Xs> {};

template <int Lower, int Upper, template <int> class Table>
struct switch_table
  : switch_<aux::tabulate<Upper - Lower + 1, Upper, Table> > {};

} // namespace metalevel

#endifs

switch_impl.hpp

/* Copyright (C) 2012 Christopher Schwaab
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
#ifdef BOOST_PP_IS_ITERATING

#define NUMBER_OF_CASES BOOST_PP_FRAME_ITERATION(1)

template <typename Xs>
struct switch_impl<NUMBER_OF_CASES, Xs> {
#   define TYPEDEF_X_SUB_I(_, i, __) \
      typedef typename boost::mpl::at_c<Xs, i>::type x_##i;
    BOOST_PP_REPEAT(NUMBER_OF_CASES, TYPEDEF_X_SUB_I, ~)

#   define METALEVEL_CASE_TABLE_ENTRY(_, i, ts) \
      case boost::mpl::first<x_##i>::type::value: \
        return boost::mpl::second<x_##i>::type::value ts ;

#   define DEFINE_CHOICE_RUN(_, argc, __) \
      template <typename R BOOST_PP_COMMA_IF(argc) \
                BOOST_PP_ENUM_PARAMS(argc, typename T)> \
      static always_inline R \
      run(int n BOOST_PP_COMMA_IF(argc) \
          BOOST_PP_ENUM_BINARY_PARAMS(argc, T, t)) { \
          switch(n) { \
          BOOST_PP_REPEAT(NUMBER_OF_CASES, \
                          METALEVEL_CASE_TABLE_ENTRY, \
                          (BOOST_PP_ENUM_PARAMS(argc, t))) \
          } \
      }
    BOOST_PP_REPEAT(METALEVEL_MAX_CHOICE_ARGS,
                    DEFINE_CHOICE_RUN, ~)

#   undef DEFINE_CHOICE_RUN
#   undef METALEVEL_CASE_TABLE_ENTRY
};

#undef NUMBER_OF_CASES 

#endif