libcruft-util/iterator/infix.hpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2010-2018 Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include "../view.hpp"

namespace cruft::iterator {
    ///////////////////////////////////////////////////////////////////////////
    /// an output iterator that inserts a delimiter between successive
    /// assignments
    ///
    /// very useful for outputting comma seperated lists to an ostream, eg:
    ///
    /// std::copy (
    ///     std::cbegin (container),
    ///     std::cend   (container),
    ///     cruft::infix_iterator<value_type> (os, ", ")
    /// );
    template <
        typename ValueT,
        class CharT = char,
        class Traits = std::char_traits<CharT>
    >
    class infix_iterator {
    public:
        using iterator_category = std::output_iterator_tag;
        using value_type = void;
        using difference_type = void;
        using reference = void;
        using pointer = void;

        using char_type    = CharT;
        using traits_type  = Traits;
        using ostream_type = std::basic_ostream<char_type, traits_type>;

        infix_iterator (ostream_type& _output, const CharT *_delimiter):
            m_output (_output),
            m_delimiter (_delimiter)
        { ; }


        infix_iterator&
        operator= (ValueT const &value)
        {
            if (!m_first)
                m_output << m_delimiter;

            m_output << value;
            m_first = false;

            return *this;
        }

        infix_iterator& operator*  (void) { return *this; }
        infix_iterator& operator++ (void) { return *this; }
        infix_iterator& operator++ (int)  { return *this; }


    private:
        bool m_first = true;
        ostream_type &m_output;
        const CharT *m_delimiter;
    };


    namespace detail {
        template <typename ContainerT, typename CharT>
        struct infix_t {
            ContainerT _container;
            const CharT *_delimiter;
        };

        template <typename ContainerT, typename CharT>
        std::ostream&
        operator<< (std::ostream &os, const infix_t<ContainerT,CharT> &val)
        {
            using iterator_type  = std::decay_t<
                decltype(std::begin (val._container))
            >;
            using value_type = typename std::iterator_traits<iterator_type >::value_type;

            std::copy (
                std::cbegin (val._container),
                std::cend   (val._container),
                infix_iterator<value_type> (os, val._delimiter)
            );

            return os;
        }
    }


    /// a helper function that returns an object that will use a
    /// cruft::infix_iterator to output a container's values to an ostream with
    /// the given delimiter.
    ///
    /// reduces boilerplate code required to output lists of things
    ///
    /// std::cout << cruft::make_infix (container) << '\n';
    template <typename ContainerT, typename CharT = char>
    auto
    make_infix (ContainerT const &_container, const CharT *_delimiter = ", ")
    {
        return detail::infix_t<ContainerT const&,CharT> { _container, _delimiter };
    }


    template <typename ContainerT, typename CharT = char>
    auto
    make_infix (ContainerT &&_container, const CharT *_delimiter = ", ")
    {
        return detail::infix_t<std::remove_reference_t<ContainerT>,CharT> {
            std::forward<ContainerT> (_container),
            _delimiter
        };
    }


    template <typename ValueT, size_t CountV, typename CharT>
    auto
    make_infix (const ValueT (&val)[CountV], CharT const *delimiter = ", ")
    {
        return make_infix (cruft::view {val}, delimiter);
    }


    template <typename ValueT, size_t CountV, typename CharT>
    auto
    make_infix (ValueT (&val)[CountV], CharT const *delimiter = ", ")
    {
        return make_infix (cruft::view {val}, delimiter);
    }
}