config.hpp

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/*
   Copyright (C) 2003 - 2016 by David White <[email protected]>
   Part of the Battle for Wesnoth Project http://www.wesnoth.org/

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY.

   See the COPYING file for more details.
*/

/**
 * @file
 * Definitions for the interface to Wesnoth Markup Language (WML).
 *
 * This module defines the interface to Wesnoth Markup Language (WML).  WML is
 * a simple hierarchical text-based file format.  The format is defined in
 * Wiki, under BuildingScenariosWML
 *
 * All configuration files are stored in this format, and data is sent across
 * the network in this format.  It is thus used extensively throughout the
 * game.
 */

#ifndef CONFIG_HPP_INCLUDED
#define CONFIG_HPP_INCLUDED

#include "global.hpp"

#include <climits>
#include <ctime>
#include <iosfwd>
#include <iterator>
#include <map>
#include <string>
#include <utility>
#include <vector>

#include <boost/exception/exception.hpp>
#include <boost/variant/apply_visitor.hpp>
#include <boost/variant/variant.hpp>

#include <boost/utility/enable_if.hpp>
#include <boost/type_traits/is_same.hpp>
#include <boost/type_traits/add_const.hpp>
#include <boost/type_traits/is_base_of.hpp>

#include "exceptions.hpp"
#include "tstring.hpp"
#include "utils/iterable_pair.hpp"

#ifdef HAVE_CXX14
#   ifdef __clang__ // Check this first, because clang also defines __GNUC__
#       ifdef __apple_build_version__ // Apple clang
#           if (__clang_major__ == 5 && __clang_minor__ >= 1) || __clang_major__ > 5 // Apple clang 5.1+
#               define USE_HETEROGENOUS_LOOKUPS
#           endif
#       else // Non-Apple clang
#           if (__clang_major__ == 3 && __clang_minor__ >= 4) || __clang_major__ > 3 // clang 3.4+
#               define USE_HETEROGENOUS_LOOKUPS
#           endif
#       endif
#   elif defined(__GNUC__) && __GNUC__ >= 5 // GCC 5.0+
#       define USE_HETEROGENOUS_LOOKUPS
#   endif
#endif

#if defined(_MSC_VER) && _MSC_VER >= 1900 // MSVC 2015
#   define USE_HETEROGENOUS_LOOKUPS
#endif

class config;
class enum_tag;

bool operator==(const config &, const config &);
inline bool operator!=(const config &a, const config &b) { return !operator==(a, b); }
std::ostream &operator << (std::ostream &, const config &);

/** A config object defines a single node in a WML file, with access to child nodes. */
class config
{
    friend bool operator==(const config& a, const config& b);
    friend struct tconfig_implementation;

    static config invalid;

    /**
     * Raises an exception if @a this is not valid.
     */
    void check_valid() const;

    /**
     * Raises an exception if @a this or @a cfg is not valid.
     */
    void check_valid(const config &cfg) const;

public:
    // Create an empty node.
    config();

    config(const config &);
    config &operator=(const config &);

    config(config &&);
    config &operator=(config &&);

    /**
     * Creates a config object with an empty child of name @a child.
     */
    explicit config(const std::string &child);

    ~config();

    // Verifies that the string can be used as an attribute or tag name
    static bool valid_id(const std::string& id);

    explicit operator bool() const
    { return this != &invalid; }

    typedef std::vector<config*> child_list;
    typedef std::map<std::string, child_list
#ifdef USE_HETEROGENOUS_LOOKUPS
        , std::less<>
#endif
    > child_map;

    struct const_child_iterator;

    struct child_iterator
    {
        typedef config value_type;
        typedef std::random_access_iterator_tag iterator_category;
        typedef int difference_type;
        typedef config *pointer;
        typedef config &reference;
        typedef child_list::iterator Itor;
        typedef child_iterator this_type;
        explicit child_iterator(const Itor &i): i_(i) {}

        child_iterator &operator++() { ++i_; return *this; }
        child_iterator operator++(int) { return child_iterator(i_++); }
        child_iterator &operator--() { --i_; return *this; }
        child_iterator operator--(int) { return child_iterator(i_--); }

        config &operator*() const { return **i_; }
        config *operator->() const { return &**i_; }

        bool operator==(const child_iterator &i) const { return i_ == i.i_; }
        bool operator!=(const child_iterator &i) const { return i_ != i.i_; }

        friend bool operator<(const this_type& a, const this_type& b) { return a.i_ < b.i_; }
        friend bool operator<=(const this_type& a, const this_type& b) { return a.i_ <= b.i_; }
        friend bool operator>=(const this_type& a, const this_type& b) { return a.i_ >= b.i_; }
        friend bool operator>(const this_type& a, const this_type& b) { return a.i_ > b.i_; }

        this_type& operator+=(Itor::difference_type n) { i_ += n; return *this; }
        this_type& operator-=(Itor::difference_type n) { i_ -= n; return *this; }

        config &operator[](Itor::difference_type n) const { return *i_[n]; }
        friend Itor::difference_type operator-(const this_type& a, const this_type& b) { return a.i_ - b.i_; }
        friend this_type operator-(const this_type& a, Itor::difference_type n) { return this_type(a.i_ - n); }
        friend this_type operator+(const this_type& a, Itor::difference_type n) { return this_type(a.i_ + n); }
        friend this_type operator+(Itor::difference_type n, const this_type& a) { return this_type(a.i_ + n); }
    private:
        Itor i_;
        friend struct const_child_iterator;
    };

    struct const_child_iterator
    {
        typedef config value_type;
        typedef std::random_access_iterator_tag iterator_category;
        typedef int difference_type;
        typedef const config *pointer;
        typedef const config &reference;
        typedef child_list::const_iterator Itor;
        typedef const_child_iterator this_type;
        explicit const_child_iterator(const Itor &i): i_(i) {}
        const_child_iterator(const child_iterator &i): i_(i.i_) {}

        const_child_iterator &operator++() { ++i_; return *this; }
        const_child_iterator operator++(int) { return const_child_iterator(i_++); }
        const_child_iterator &operator--() { --i_; return *this; }
        const_child_iterator operator--(int) { return const_child_iterator(i_--); }

        const config &operator*() const { return **i_; }
        const config *operator->() const { return &**i_; }

        bool operator==(const const_child_iterator &i) const { return i_ == i.i_; }
        bool operator!=(const const_child_iterator &i) const { return i_ != i.i_; }

        friend bool operator<(const this_type& a, const this_type& b) { return a.i_ < b.i_; }
        friend bool operator<=(const this_type& a, const this_type& b) { return a.i_ <= b.i_; }
        friend bool operator>=(const this_type& a, const this_type& b) { return a.i_ >= b.i_; }
        friend bool operator>(const this_type& a, const this_type& b) { return a.i_ > b.i_; }

        this_type& operator+=(Itor::difference_type n) { i_ += n; return *this; }
        this_type& operator-=(Itor::difference_type n) { i_ -= n; return *this; }

        const config &operator[](Itor::difference_type n) const { return *i_[n]; }
        friend Itor::difference_type operator-(const this_type& a, const this_type& b) { return a.i_ - b.i_; }
        friend this_type operator-(const this_type& a, Itor::difference_type n) { return this_type(a.i_ - n); }
        friend this_type operator+(const this_type& a, Itor::difference_type n) { return this_type(a.i_ + n); }
        friend this_type operator+(Itor::difference_type n, const this_type& a) { return this_type(a.i_ + n); }

    private:
        Itor i_;
    };

    typedef std::pair<child_iterator,child_iterator> child_itors;
    typedef std::pair<const_child_iterator,const_child_iterator> const_child_itors;

    /**
     * Variant for storing WML attributes.
     * The most efficient type is used when assigning a value. For instance,
     * strings "yes", "no", "true", "false" will be detected and stored as boolean.
     * @note The blank variant is only used when querying missing attributes.
     *       It is not stored in config objects.
     */
    class attribute_value
    {
        /// A wrapper for bool to get the correct streaming ("true"/"false").
        /// Most visitors can simply treat this as bool.
    public:
        class true_false
        {
            bool value_;
        public:
            explicit true_false(bool value = false) : value_(value) {}
            operator bool() const { return value_; }

            const std::string & str() const
            { return value_ ? config::attribute_value::s_true :
                              config::attribute_value::s_false; }
        };
        friend std::ostream& operator<<(std::ostream &os, const true_false &v);

        /// A wrapper for bool to get the correct streaming ("yes"/"no").
        /// Most visitors can simply treat this as bool.
        class yes_no
        {
            bool value_;
        public:
            explicit yes_no(bool value = false) : value_(value) {}
            operator bool() const { return value_; }

            const std::string & str() const
            { return value_ ? config::attribute_value::s_yes :
                              config::attribute_value::s_no; }
        };
        friend std::ostream& operator<<(std::ostream &os, const yes_no &v);
    private:
        /// Visitor for checking equality.
        class equality_visitor;
        /// Visitor for converting a variant to a string.
        class string_visitor;

        // Data will be stored in a variant, allowing for the possibility of
        // boolean, numeric, and translatable data in addition to basic string
        // data. For most purposes, int is the preferred type for numeric data
        // as it is fast (often natural word size). While it is desirable to
        // use few types (to keep the overhead low), we do have use cases for
        // fractions (double) and huge numbers (up to the larger of LLONG_MAX
        // and SIZE_MAX).
        typedef boost::variant<boost::blank,
                               true_false, yes_no,
                               int, unsigned long long, double,
                               std::string, t_string
                              > value_type;
        /// The stored value will always use the first type from the variant
        /// definition that can represent it and that can be streamed to the
        /// correct string representation (if applicable).
        /// This is enforced upon assignment.
        value_type value_;

    public:
        /// Default implementation, but defined out-of-line for efficiency reasons.
        attribute_value();
        /// Default implementation, but defined out-of-line for efficiency reasons.
        ~attribute_value();
        /// Default implementation, but defined out-of-line for efficiency reasons.
        attribute_value(const attribute_value &);
        /// Default implementation, but defined out-of-line for efficiency reasons.
        attribute_value &operator=(const attribute_value &);

        // Numeric assignments:
        attribute_value &operator=(bool v);
        attribute_value &operator=(int v);
        attribute_value &operator=(long v)          { return operator=(static_cast<long long>(v)); }
        attribute_value &operator=(long long v);
        attribute_value &operator=(unsigned v)      { return operator=(static_cast<unsigned long long>(v)); }
        attribute_value &operator=(unsigned long v) { return operator=(static_cast<unsigned long long>(v)); }
        attribute_value &operator=(unsigned long long v);
        attribute_value &operator=(double v);

        // String assignments:
        attribute_value &operator=(const char *v)   { return operator=(std::string(v)); }
        attribute_value &operator=(const std::string &v);
        attribute_value &operator=(const t_string &v);
        template<typename T>
        typename boost::enable_if<boost::is_base_of<enum_tag, T>, attribute_value &>::type operator=(const T &v)
        {
            return operator=(T::enum_to_string(v));
        }
        // Extracting as a specific type:
        bool to_bool(bool def = false) const;
        int to_int(int def = 0) const;
        long long to_long_long(long long def = 0) const;
        unsigned to_unsigned(unsigned def = 0) const;
        size_t to_size_t(size_t def = 0) const;
        time_t to_time_t(time_t def = 0) const;
        double to_double(double def = 0.) const;
        std::string str() const;
        t_string t_str() const;
        /**
            @param T a type created with MAKE_ENUM macro
            NOTE: since T::VALUE constants is not of type T but of the underlying enum type you must specify the template parameter explicitly
            TODO: Fix this in c++11 using constexpr types.
        */
        template<typename T>
        typename boost::enable_if<boost::is_base_of<enum_tag, T>, T>::type to_enum(const T &v) const
        {
            return T::string_to_enum(this->str(), v);
        }

        // Implicit conversions:
        operator int() const { return to_int(); }
        operator std::string() const { return str(); }
        operator t_string() const { return t_str(); }

        /// Tests for an attribute that was never set.
        bool blank() const;
        /// Tests for an attribute that either was never set or was set to "".
        bool empty() const;


        // Comparisons:
        bool operator==(const attribute_value &other) const;
        bool operator!=(const attribute_value &other) const
        { return !operator==(other); }

        bool equals(const std::string& str) const;
        // These function prevent t_string creation in case of c["a"] == "b" comparisons.
        // The templates are needed to prevent using these function in case of c["a"] == 0 comparisons.
        template<typename T>
        typename boost::enable_if<boost::is_same<const std::string, typename boost::add_const<T>::type>, bool>::type
        friend operator==(const attribute_value &val, const T &str)
        { return val.equals(str); }

        template<typename T>
        typename boost::enable_if<boost::is_same<const char*, T>, bool>::type
        friend operator==(const attribute_value &val, T str)
        { return val.equals(std::string(str)); }

        template<typename T>
        bool friend operator==(const T &str, const attribute_value &val)
        { return val == str; }

        template<typename T>
        bool friend operator!=(const attribute_value &val, const T &str)
        { return !(val == str); }

        template<typename T>
        bool friend operator!=(const T &str, const attribute_value &val)
        { return !(val == str); }

        // Streaming:
        friend std::ostream& operator<<(std::ostream &os, const attribute_value &v);

        // Visitor support:
        /// Applies a visitor to the underlying variant.
        /// (See the documentation for Boost.Variant.)
        template <typename V>
        typename V::result_type apply_visitor(const V & visitor) const
        { return boost::apply_visitor(visitor, value_); }

    private:
        // Special strings.
        static const std::string s_yes, s_no;
        static const std::string s_true, s_false;
    };

    typedef std::map<
        std::string
        , attribute_value
#ifdef USE_HETEROGENOUS_LOOKUPS
        , std::less<>
#endif
    > attribute_map;
    typedef attribute_map::value_type attribute;

    struct const_attribute_iterator
    {
        typedef attribute value_type;
        typedef std::forward_iterator_tag iterator_category;
        typedef int difference_type;
        typedef const attribute *pointer;
        typedef const attribute &reference;
        typedef attribute_map::const_iterator Itor;
        explicit const_attribute_iterator(const Itor &i): i_(i) {}

        const_attribute_iterator &operator++() { ++i_; return *this; }
        const_attribute_iterator operator++(int) { return const_attribute_iterator(i_++); }

        const attribute &operator*() const { return *i_; }
        const attribute *operator->() const { return &*i_; }

        bool operator==(const const_attribute_iterator &i) const { return i_ == i.i_; }
        bool operator!=(const const_attribute_iterator &i) const { return i_ != i.i_; }

    private:
        Itor i_;
    };

    typedef std::pair<const_attribute_iterator,const_attribute_iterator> const_attr_itors;

    child_itors child_range(const std::string& key);
    const_child_itors child_range(const std::string& key) const;
    unsigned child_count(const std::string &key) const;
    unsigned all_children_count() const;
    /** Note: this function also counts the 'blank' attributes, so it might return more than one might expect */
    unsigned attribute_count() const
    { return values.size(); }

    /**
     * Determine whether a config has a child or not.
     *
     * @param key                 The key of the child to find.
     *
     * @returns                   Whether a child is available.
     */
    bool has_child(const std::string& key) const;

    /**
     * Returns the first child with the given @a key, or an empty config if there is none.
     */
    const config & child_or_empty(const std::string &key) const;

    /**
     * Returns the nth child with the given @a key, or
     * a reference to an invalid config if there is none.
     * @note A negative @a n accesses from the end of the object.
     *       For instance, -1 is the index of the last child.
     */
    config &child(const std::string& key, int n = 0);

#ifdef USE_HETEROGENOUS_LOOKUPS
    template<int N>
    config &child(const char(&key)[N], int n = 0)
    { return child_impl(key, N - 1, n); }
private:
    config &child_impl(const char* key, int len, int n = 0);
public:
#endif
    /**
     * Returns the nth child with the given @a key, or
     * a reference to an invalid config if there is none.
     * @note A negative @a n accesses from the end of the object.
     *       For instance, -1 is the index of the last child.
     */
    const config &child(const std::string& key, int n = 0) const
    { return const_cast<config *>(this)->child(key, n); }

#ifdef USE_HETEROGENOUS_LOOKUPS
    template<int N>
    const config &child(const char(&key)[N], int n = 0) const
    { return const_cast<config *>(this)->child_impl(key, N- 1, n); }
#endif
    /**
     * Returns a mandatory child node.
     *
     * If the child is not found a @ref wml_exception is thrown.
     *
     * @pre                       parent[0] == '['
     * @pre                       parent[parent.size() - 1] == ']'
     *
     * @param key                 The key of the child item to return.
     * @param parent              The section in which the child should reside.
     *                            This is only used for error reporting.
     *
     * @returns                   The wanted child node.
     */
    config& child(const std::string& key, const std::string& parent);

    /**
     * Returns a mandatory child node.
     *
     * If the child is not found a @ref wml_exception is thrown.
     *
     * @pre                       parent[0] == '['
     * @pre                       parent[parent.size() - 1] == ']'
     *
     * @param key                 The key of the child item to return.
     * @param parent              The section in which the child should reside.
     *                            This is only used for error reporting.
     *
     * @returns                   The wanted child node.
     */
    const config& child(
              const std::string& key
            , const std::string& parent) const;

    config& add_child(const std::string& key);
    config& add_child(const std::string& key, const config& val);
    config& add_child_at(const std::string &key, const config &val, unsigned index);

    config &add_child(const std::string &key, config &&val);

    /**
     * Returns a reference to the attribute with the given @a key.
     * Creates it if it does not exist.
     */
    attribute_value &operator[](const std::string &key);

    /**
     * Returns a reference to the attribute with the given @a key
     * or to a dummy empty attribute if it does not exist.
     */
    const attribute_value &operator[](const std::string &key) const;

#ifdef USE_HETEROGENOUS_LOOKUPS
    /**
     * Returns a reference to the attribute with the given @a key
     * or to a dummy empty attribute if it does not exist.
     */
    template<int N>
    inline const attribute_value &operator[](const char (&key)[N]) const
    {
        //-1 for the terminating null character.
        return get_attribute(key, N - 1);
    }

    template<int N>
    inline attribute_value& operator[](const char (&key)[N])
    {
        return (*this)[std::string(key)];
    }
#endif
    /**
     * Returns a pointer to the attribute with the given @a key
     * or nullptr if it does not exist.
     */
    const attribute_value *get(const std::string &key) const;

    /**
     * Function to handle backward compatibility
     * Get the value of key and if missing try old_key
     * and log msg as a WML error (if not empty)
    */
    const attribute_value &get_old_attribute(const std::string &key, const std::string &old_key, const std::string& msg = "") const;
    /**
     * Returns a reference to the first child with the given @a key.
     * Creates the child if it does not yet exist.
     */
    config &child_or_add(const std::string &key);

    bool has_attribute(const std::string &key) const;
    /**
     * Function to handle backward compatibility
     * Check if has key or old_key
     * and log msg as a WML error (if not empty)
    */
    bool has_old_attribute(const std::string &key, const std::string &old_key, const std::string& msg = "") const;

    void remove_attribute(const std::string &key);
    void merge_attributes(const config &);
    template<typename... T>
    void remove_attributes(T... keys) {
        for(const std::string& key : {keys...}) {
            remove_attribute(key);
        }
    }

    const_attr_itors attribute_range() const;

    /**
     * Returns the first child of tag @a key with a @a name attribute
     * containing @a value.
     */
    config &find_child(const std::string &key, const std::string &name,
        const std::string &value);

    const config &find_child(const std::string &key, const std::string &name,
        const std::string &value) const
    { return const_cast<config *>(this)->find_child(key, name, value); }

    void clear_children(const std::string& key);
    template<typename... T>
    void clear_children(T... keys) {
        for(std::string key : {keys...}) {
            clear_children(key);
        }
    }

    /**
     * Moves all the children with tag @a key from @a src to this.
     */
    void splice_children(config &src, const std::string &key);

    void remove_child(const std::string &key, unsigned index);
    void recursive_clear_value(const std::string& key);

    void clear();
    bool empty() const;

    std::string debug() const;
    std::string hash() const;

    struct error : public game::error, public boost::exception {
        error(const std::string& message) : game::error(message) {}
    };

    struct child_pos
    {
        child_pos(child_map::iterator p, unsigned i) : pos(p), index(i) {}
        child_map::iterator pos;
        unsigned index;

        bool operator==(const child_pos& o) const { return pos == o.pos && index == o.index; }
        bool operator!=(const child_pos& o) const { return !operator==(o); }
    };

    struct any_child
    {
        const child_map::key_type &key;
        const config &cfg;
        any_child(const child_map::key_type *k, const config *c): key(*k), cfg(*c) {}
    };

    struct all_children_iterator
    {
        struct arrow_helper
        {
            any_child data;
            arrow_helper(const all_children_iterator &i): data(*i) {}
            const any_child *operator->() const { return &data; }
        };

        typedef any_child value_type;
        typedef std::forward_iterator_tag iterator_category;
        typedef int difference_type;
        typedef const arrow_helper pointer;
        typedef const any_child reference;
        typedef std::vector<child_pos>::const_iterator Itor;
        explicit all_children_iterator(const Itor &i): i_(i) {}

        all_children_iterator &operator++() { ++i_; return *this; }
        all_children_iterator operator++(int) { return all_children_iterator(i_++); }

        reference operator*() const;
        pointer operator->() const { return *this; }

        bool operator==(const all_children_iterator &i) const { return i_ == i.i_; }
        bool operator!=(const all_children_iterator &i) const { return i_ != i.i_; }

    private:
        Itor i_;

        friend class config;
    };

    typedef std::pair<all_children_iterator, all_children_iterator> all_children_itors;

    /** In-order iteration over all children. */
    all_children_itors all_children_range() const;

    all_children_iterator ordered_begin() const;
    all_children_iterator ordered_end() const;
    all_children_iterator erase(const all_children_iterator& i);

    /**
     * A function to get the differences between this object,
     * and 'c', as another config object.
     * I.e. calling cfg2.apply_diff(cfg1.get_diff(cfg2))
     * will make cfg2 identical to cfg1.
     */
    config get_diff(const config& c) const;
    void get_diff(const config& c, config& res) const;

    /**
     * The name of the attribute used for tracking diff changes
     */
    static const char* diff_track_attribute;

    /**
     * A function to apply a diff config onto this config object.
     *
     * If the "track" parameter is true, the changes made will be marked in a
     * magic attribute (defined above) of this and child nodes of this config,
     * with "new" value indicating an added child, "modified" a modified one,
     * and "deleted" for the deleted items, *which will not be actually
     * deleted* (so calling code can easily see what they are).
     * Use clear_diff_track with the same diff object to clear the tracking
     * info and actually delete the nodes.
     */
    void apply_diff(const config& diff, bool track = false); //throw error

    /**
     * Clear any tracking info from a previous apply_diff call with tracking.
     * This also removes the nodes that are to be deleted, in effect making
     * apply_diff(c, true); clear_diff_tracking(c);
     * equivalent to apply_diff(c, false);
     */
    void clear_diff_track(const config& diff);

    /**
     * Merge config 'c' into this config, overwriting this config's values.
     */
    void merge_with(const config& c);

    /**
     * Merge config 'c' into this config, preserving this config's values.
     */
    void inherit_from(const config& c);

    bool matches(const config &filter) const;

    /**
     * Append data from another config object to this one.
     * Attributes in the latter config object will clobber attributes in this one.
     */
    void append(const config& cfg);

    /**
     * Adds children from @a cfg.
     */
    void append_children(const config &cfg);

    /**
     * Adds children from @a cfg.
     */
    void append_children(const config &cfg, const std::string& key);

    /**
     * Adds attributes from @a cfg.
     */
    void append_attributes(const config &cfg);

    /**
     * All children with the given key will be merged
     * into the first element with that key.
     */
    void merge_children(const std::string& key);

    /**
     * All children with the given key and with equal values
     * of the specified attribute will be merged into the
     * element with that key and that value of the attribute
     */
    void merge_children_by_attribute(const std::string& key, const std::string& attribute);

    //this is a cheap O(1) operation
    void swap(config& cfg);

private:
#ifdef USE_HETEROGENOUS_LOOKUPS
    const attribute_value& get_attribute(const char* key, int len) const;
#endif
    /**
     * Removes the child at position @a pos of @a l.
     */
    std::vector<child_pos>::iterator remove_child(const child_map::iterator &l, unsigned pos);

    /** All the attributes of this node. */
    attribute_map values;

    /** A list of all children of this node. */
    child_map children;

    std::vector<child_pos> ordered_children;
};

class variable_set
{
public:
    virtual ~variable_set() {}
    virtual config::attribute_value get_variable_const(const std::string &id) const = 0;
};

inline std::ostream &operator<<(std::ostream &os, const config::attribute_value::true_false &v) { return os << v.str(); }
inline std::ostream &operator<<(std::ostream &os, const config::attribute_value::yes_no &v)     { return os << v.str(); }

#endif