Adaptor to permit range based iteration via non-conforming begin-expr, end-expr ranges

const-range-adaptor.hh

/* vim: set et ft=cpp.doxygen sts=2 sw=2 ts=8 : */
/**
 * Copyright © 2013 Saleem Abdulrasool <[email protected]>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
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 **/

#ifndef const_range_adaptor_hh
#define const_range_adaptor_hh

template <typename type_,
          typename const_iterator_type_ = typename type_::const_iterator,
          const_iterator_type_ (type_::*begin_expr_)() const = &type_::begin,
          const_iterator_type_ (type_::*end_expr_)() const = &type_::end>
class const_range_adaptor {
 public:
  constexpr const_range_adaptor(const type_ & iterable) noexcept
    : iterable_(iterable) {}
  const_iterator_type_ begin() const { return (iterable_.*begin_expr_)(); }
  const_iterator_type_ end() const { return (iterable_.*end_expr_)(); }
 private:
  const type_ & iterable_;
};

#endif

example.cc

#include "const-range-adaptor.hh"

#include <cstdlib>
#include <iostream>
#include <vector>

struct multi_iteration_model {
  std::vector<int> integers_;
  std::vector<char> characters_;

  multi_iteration_model() noexcept
    : integers_{ 1, 2, 3, 4, 5 },
      characters_{ 'a', 'b', 'c', 'd' } {}

  std::vector<int>::const_iterator begin_integers() const {
    return integers_.begin();
  }
  std:vector<int>::const_iterator end_integers() const {
    return integers_.end();
  }
  
  std::vector<char>::const_iterator begin_characters() const {
    return characters_.begin();
  }
  std:vector<char>::const_iterator end_characters() const {
    return characters_.end();
  }
};

const_range_adapter<multi_iteration_model, std::vector<int>::const_iterator,
                    &multi_iteration_model::begin_integers,
                    &multi_iteration_model::end_integers>
integers(const multi_iteration_model & mim) {
  return const_range_adapter<multi_iteration_model,
                             std::vector<int>::const_iterator,
                             &multi_iteration_model::begin_integers,
                             &multi_iteration_model::end_integers>(mim);
}

const_range_adapter<multi_iterator_model, std::vector<char>::const_iterator,
                    &multi_iteration_model::begin_characters,
                    &multi_iteration_model::end_characters>
characters(const multi_iteration_model & mim) {
  return const_range_adapter<multi_iteration_model,
                             std::vector<char>::const_iterator,
                             &multi_iteration_model::begin_characters,
                             &multi_iteration_model::end_characters>(mim);
}

int main(int, char **) {
  multi_iteration_model mim;
  for (const auto & integer : integers(mim))
    std::cout << "integer: " << integer << std::endl;
  for (const auto & character : characters(mim))
    std::cout << "character: " << character << std::endl;
  return EXIT_SUCCESS;
}