test/format

// Formatting library for C++ - the standard API implementation
//
// Copyright (c) 2012 - present, Victor Zverovich
// All rights reserved.
//
// For the license information refer to format.h.

#ifndef FMT_FORMAT_
#define FMT_FORMAT_

#include <cassert>
#include <variant>
#include "fmt/format.h"

// This implementation verifies the correctness of the standard API proposed in
// P0645 Text Formatting and is optimized for copy-pasting from the paper, not
// for efficiency or readability. An efficient implementation should not use
// std::variant and should store packed argument type tags separately from
// values in basic_format_args for small number of arguments.

namespace std {
template<class T>
constexpr bool Integral = is_integral_v<T>;

template <class O>
  using iter_difference_t = ptrdiff_t;
}

// https://fmt.dev/Text%20Formatting.html#format.syn
namespace std {
  // [format.error], class format_error
  class format_error;

  // [format.formatter], formatter
  template<class charT> class basic_format_parse_context;
  using format_parse_context = basic_format_parse_context<char>;
  using wformat_parse_context = basic_format_parse_context<wchar_t>;
  
  template<class Out, class charT> class basic_format_context;
  using format_context = basic_format_context<
    /* unspecified */ std::back_insert_iterator<fmt::internal::buffer<char>>, char>;
  using wformat_context = basic_format_context<
    /* unspecified */ std::back_insert_iterator<fmt::internal::buffer<wchar_t>>, wchar_t>;

  template<class T, class charT = char> struct formatter {
    formatter() = delete;
  };
  
  // [format.arguments], arguments
  template<class Context> class basic_format_arg;

  template<class Visitor, class Context>
    /* see below */ auto visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg);

  template<class Context, class... Args> struct format_arg_store; // exposition only

  template<class Context> class basic_format_args;
  using format_args = basic_format_args<format_context>;
  using wformat_args = basic_format_args<wformat_context>;

  template<class Out, class charT>
    using format_args_t = basic_format_args<basic_format_context<Out, charT>>;

  template<class Context = format_context, class... Args>
    format_arg_store<Context, Args...>
      make_format_args(const Args&... args);
  template<class... Args>
    format_arg_store<wformat_context, Args...>
      make_wformat_args(const Args&... args);

  // [format.functions], formatting functions
  template<class... Args>
    string format(string_view fmt, const Args&... args);
  template<class... Args>
    wstring format(wstring_view fmt, const Args&... args);

  string vformat(string_view fmt, format_args args);
  wstring vformat(wstring_view fmt, wformat_args args);

  template<class Out, class... Args>
    Out format_to(Out out, string_view fmt, const Args&... args);
  template<class Out, class... Args>
    Out format_to(Out out, wstring_view fmt, const Args&... args);

  template<class Out>
    Out vformat_to(Out out, string_view fmt, format_args_t<Out, char> args);
  template<class Out>
    Out vformat_to(Out out, wstring_view fmt, format_args_t<Out, wchar_t> args);

  template<class Out>
    struct format_to_n_result {
      Out out;
      iter_difference_t<Out> size;
    };
  
  template<class Out, class... Args>
    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
                                        string_view fmt, const Args&... args);
  template<class Out, class... Args>
    format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
                                        wstring_view fmt, const Args&... args);

  template<class... Args>
    size_t formatted_size(string_view fmt, const Args&... args);
  template<class... Args>
    size_t formatted_size(wstring_view fmt, const Args&... args);
}

// https://fmt.dev/Text%20Formatting.html#format.error
namespace std {
  class format_error : public runtime_error {
  public:
    explicit format_error(const string& what_arg) : runtime_error(what_arg) {}
    explicit format_error(const char* what_arg) : runtime_error(what_arg) {}
  };
}

namespace std {
namespace detail {
struct error_handler {
  // This function is intentionally not constexpr to give a compile-time error.
  void on_error(const char* message) {
    throw std::format_error(message);
  }
};
}
}

// https://fmt.dev/Text%20Formatting.html#format.parse_context
namespace std {
  template<class charT>
  class basic_format_parse_context {
  public:
    using char_type = charT;
    using const_iterator = typename basic_string_view<charT>::const_iterator;
    using iterator = const_iterator;

  private:
    iterator begin_;                              // exposition only
    iterator end_;                                // exposition only
    enum indexing { unknown, manual, automatic }; // exposition only
    indexing indexing_;                           // exposition only
    size_t next_arg_id_;                          // exposition only
    size_t num_args_;                             // exposition only

  public:
    explicit constexpr basic_format_parse_context(basic_string_view<charT> fmt,
                                                  size_t num_args = 0) noexcept;
    basic_format_parse_context(const basic_format_parse_context&) = delete;
    basic_format_parse_context& operator=(const basic_format_parse_context&) = delete;

    constexpr const_iterator begin() const noexcept;
    constexpr const_iterator end() const noexcept;
    constexpr void advance_to(const_iterator it);

    constexpr size_t next_arg_id();
    constexpr void check_arg_id(size_t id);

    // Implementation detail:
    constexpr void check_arg_id(fmt::string_view) {}
    detail::error_handler error_handler() const { return {}; }
    void on_error(const char* msg) { error_handler().on_error(msg); }
  };
}

namespace std {
template<class charT>
/* explicit */ constexpr basic_format_parse_context<charT>::
                   basic_format_parse_context(basic_string_view<charT> fmt,
                                              size_t num_args) noexcept
: begin_(fmt.begin()), end_(fmt.end()), indexing_(unknown), next_arg_id_(0), num_args_(num_args) {}

template<class charT>
constexpr typename basic_format_parse_context<charT>::const_iterator basic_format_parse_context<charT>::begin() const noexcept { return begin_; }

template<class charT>
constexpr typename basic_format_parse_context<charT>::const_iterator basic_format_parse_context<charT>::end() const noexcept { return end_; }

template<class charT>
constexpr void basic_format_parse_context<charT>::advance_to(typename basic_format_parse_context<charT>::iterator it) { begin_ = it; }

template<class charT>
constexpr size_t basic_format_parse_context<charT>::next_arg_id() {
  if (indexing_ == manual)
    throw format_error("manual to automatic indexing");
  if (indexing_ == unknown)
    indexing_ = automatic;
  return next_arg_id_++;
}

template<class charT>
constexpr void basic_format_parse_context<charT>::check_arg_id(size_t id) {
  // clang doesn't support __builtin_is_constant_evaluated yet
  //if (!(!__builtin_is_constant_evaluated() || id < num_args_))
  //  throw format_error(invalid index is out of range");
  if (indexing_ == automatic)
    throw format_error("automatic to manual indexing");
  if (indexing_ == unknown)
    indexing_ = manual;
}
}

// https://fmt.dev/Text%20Formatting.html#format.context
namespace std {
  template<class Out, class charT>
  class basic_format_context {
    basic_format_args<basic_format_context> args_; // exposition only
    Out out_;                                      // exposition only

  public:
    using iterator = Out;
    using char_type = charT;
    template<class T> using formatter_type = formatter<T, charT>;

    basic_format_arg<basic_format_context> arg(size_t id) const;

    iterator out();
    void advance_to(iterator it);

    // Implementation details:
    using format_arg = basic_format_arg<basic_format_context>;
    basic_format_context(Out out, basic_format_args<basic_format_context> args, fmt::internal::locale_ref)
    : args_(args), out_(out) {}
    detail::error_handler error_handler() const { return {}; }
    basic_format_arg<basic_format_context> arg(fmt::basic_string_view<charT>) const {
      return {}; // unused: named arguments are not supported yet
    }
    void on_error(const char* msg) { error_handler().on_error(msg); }
  };
}

namespace std {
template<class O, class charT>
basic_format_arg<basic_format_context<O, charT>> basic_format_context<O, charT>::arg(size_t id) const { return args_.get(id); }

template<class O, class charT>
typename basic_format_context<O, charT>::iterator basic_format_context<O, charT>::out() { return out_; }

template<class O, class charT>
void basic_format_context<O, charT>::advance_to(typename basic_format_context<O, charT>::iterator it) { out_ = it; }
}

namespace std {
namespace detail {
template <typename T>
constexpr bool is_standard_integer_v =
    std::is_same_v<T, signed char> ||
    std::is_same_v<T, short int> ||
    std::is_same_v<T, int> ||
    std::is_same_v<T, long int> ||
    std::is_same_v<T, long long int>;

template <typename T>
constexpr bool is_standard_unsigned_integer_v =
    std::is_same_v<T, unsigned char> ||
    std::is_same_v<T, unsigned short int> ||
    std::is_same_v<T, unsigned int> ||
    std::is_same_v<T, unsigned long int> ||
    std::is_same_v<T, unsigned long long int>;

template <typename T, typename Char> struct formatter;
}
}

// https://fmt.dev/Text%20Formatting.html#format.arg
namespace std {
  template<class Context>
  class basic_format_arg {
  public:
    class handle;

  private:
    using char_type = typename Context::char_type;                       // exposition only

    variant<monostate, bool, char_type,
            int, unsigned int, long long int, unsigned long long int,
            double, long double,
            const char_type*, basic_string_view<char_type>,
            const void*, handle> value;                                  // exposition only

    template<typename T,
      typename = enable_if_t<
        std::is_same_v<T, bool> ||
        std::is_same_v<T, char_type> ||
        (std::is_same_v<T, char> && std::is_same_v<char_type, wchar_t>) ||
        detail::is_standard_integer_v<T> ||
        detail::is_standard_unsigned_integer_v<T> ||
        sizeof(typename Context::template formatter_type<T>().format(declval<const T&>(), declval<Context&>())) != 0
    >> explicit basic_format_arg(const T& v) noexcept; // exposition only
    explicit basic_format_arg(float n) noexcept;                         // exposition only
    explicit basic_format_arg(double n) noexcept;                        // exposition only
    explicit basic_format_arg(long double n) noexcept;                   // exposition only
    explicit basic_format_arg(const char_type* s);                       // exposition only

    template<class traits>
      explicit basic_format_arg(
        basic_string_view<char_type, traits> s) noexcept;                // exposition only

    template<class traits, class Allocator>
      explicit basic_format_arg(
        const basic_string<char_type, traits, Allocator>& s) noexcept;   // exposition only

    explicit basic_format_arg(nullptr_t) noexcept;                       // exposition only

    template<class T, typename = enable_if_t<is_void_v<T>>>
      explicit basic_format_arg(const T* p) noexcept;                    // exposition only

    // Fails due to a bug in clang
    //template<class Visitor, class Ctx>
    //  friend auto visit_format_arg(Visitor&& vis,
    //                                    basic_format_arg<Ctx> arg);           // exposition only

    friend auto get_value(basic_format_arg arg) {
      return arg.value;
    }

    template <typename T, typename Char> friend struct detail::formatter;

    template<class Ctx, class... Args>
      friend format_arg_store<Ctx, Args...>
        make_format_args(const Args&... args);                           // exposition only

  public:
    basic_format_arg() noexcept;

    explicit operator bool() const noexcept;
  };
}

namespace std {
template<class Context>
basic_format_arg<Context>::basic_format_arg() noexcept {}

template<class Context>
template<class T, typename> /* explicit */ basic_format_arg<Context>::basic_format_arg(const T& v) noexcept {
  if constexpr (std::is_same_v<T, bool> || std::is_same_v<T, char_type>)
    value = v;
  else if constexpr (std::is_same_v<T, char> && std::is_same_v<char_type, wchar_t>)
    value = static_cast<wchar_t>(v);
  else if constexpr (detail::is_standard_integer_v<T> && sizeof(T) <= sizeof(int))
    value = static_cast<int>(v);
  else if constexpr (detail::is_standard_unsigned_integer_v<T> && sizeof(T) <= sizeof(unsigned))
    value = static_cast<unsigned>(v);
  else if constexpr (detail::is_standard_integer_v<T>)
    value = static_cast<long long int>(v);
  else if constexpr (detail::is_standard_unsigned_integer_v<T>)
    value = static_cast<unsigned long long int>(v);
  else if constexpr (sizeof(typename Context::template formatter_type<T>().format(declval<const T&>(), declval<Context&>())) != 0)
    value = handle(v);
}

template<class Context>
/* explicit */ basic_format_arg<Context>::basic_format_arg(float n) noexcept
  : value(static_cast<double>(n)) {}

template<class Context>
/* explicit */ basic_format_arg<Context>::basic_format_arg(double n) noexcept
  : value(n) {}

template<class Context>
/* explicit */ basic_format_arg<Context>::basic_format_arg(long double n) noexcept
  : value(n) {}

template<class Context>
/* explicit */ basic_format_arg<Context>::basic_format_arg(const typename basic_format_arg<Context>::char_type* s)
  : value(s) {
  assert(s != nullptr);
}

template<class Context>
template<class traits>
/* explicit */ basic_format_arg<Context>::basic_format_arg(basic_string_view<char_type, traits> s) noexcept
  : value(s) {}

template<class Context>
template<class traits, class Allocator>
/* explicit */ basic_format_arg<Context>::basic_format_arg(
    const basic_string<char_type, traits, Allocator>& s) noexcept
  : value(basic_string_view<char_type>(s.data(), s.size())) {}


template<class Context>
/* explicit */ basic_format_arg<Context>::basic_format_arg(nullptr_t) noexcept
  : value(static_cast<const void*>(nullptr)) {}

template<class Context>
template<class T, typename> /* explicit */ basic_format_arg<Context>::basic_format_arg(const T* p) noexcept
  : value(p) {}

template<class Context>
/* explicit */ basic_format_arg<Context>::operator bool() const noexcept {
    return !holds_alternative<monostate>(value);
}
}

namespace std {
  template<class Context>
  class basic_format_arg<Context>::handle {
    const void* ptr_;                                         // exposition only
    void (*format_)(basic_format_parse_context<char_type>&,
                    Context&, const void*);                   // exposition only

    template<class T> explicit handle(const T& val) noexcept; // exposition only

    friend class basic_format_arg<Context>;                   // exposition only

  public:
    void format(basic_format_parse_context<char_type>&, Context& ctx) const;
  };
}

namespace std {
template<class Context>
template<class T> /* explicit */ basic_format_arg<Context>::handle::handle(const T& val) noexcept
  : ptr_(&val), format_([](basic_format_parse_context<char_type>& parse_ctx, Context& format_ctx, const void* ptr) {
    typename Context::template formatter_type<T> f;
    parse_ctx.advance_to(f.parse(parse_ctx));
    format_ctx.advance_to(f.format(*static_cast<const T*>(ptr), format_ctx));
  }) {}

template<class Context>
void basic_format_arg<Context>::handle::format(basic_format_parse_context<char_type>& parse_ctx, Context& format_ctx) const {
  format_(parse_ctx, format_ctx, ptr_);
}

// https://fmt.dev/Text%20Formatting.html#format.visit
template<class Visitor, class Context>
  auto visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg) {
    return visit(vis, get_value(arg));
  }
}

// https://fmt.dev/Text%20Formatting.html#format.store
namespace std {
  template<class Context, class... Args>
  struct format_arg_store { // exposition only
    array<basic_format_arg<Context>, sizeof...(Args)> args;
  };
}

// https://fmt.dev/Text%20Formatting.html#format.basic_args
namespace std {
  template<class Context>
  class basic_format_args {
    size_t size_;                           // exposition only
    const basic_format_arg<Context>* data_; // exposition only

  public:
    basic_format_args() noexcept;

    template<class... Args>
      basic_format_args(const format_arg_store<Context, Args...>& store) noexcept;

    basic_format_arg<Context> get(size_t i) const noexcept;
  };
}

namespace std {

template<class Context>
basic_format_args<Context>::basic_format_args() noexcept : size_(0) {}

template<class Context>
template<class... Args>
  basic_format_args<Context>::basic_format_args(const format_arg_store<Context, Args...>& store) noexcept
  : size_(sizeof...(Args)), data_(store.args.data()) {}

template<class Context>
basic_format_arg<Context> basic_format_args<Context>::get(size_t i) const noexcept {
  return i < size_ ? data_[i] : basic_format_arg<Context>();
}
}

namespace std {
// https://fmt.dev/Text%20Formatting.html#format.make_args
template<class Context /*= format_context*/, class... Args>
  format_arg_store<Context, Args...> make_format_args(const Args&... args) {
    return {basic_format_arg<Context>(args)...};
  }

// https://fmt.dev/Text%20Formatting.html#format.make_wargs
template<class... Args>
  format_arg_store<wformat_context, Args...> make_wformat_args(const Args&... args) {
    return make_format_args<wformat_context>(args...);
  }
}

namespace std {
namespace detail {

template <typename Range>
class arg_formatter
    : public fmt::internal::arg_formatter_base<Range, error_handler> {
 private:
  using char_type = typename Range::value_type;
  using base = fmt::internal::arg_formatter_base<Range, error_handler>;
  using format_context = std::basic_format_context<typename base::iterator, char_type>;
  using parse_context = basic_format_parse_context<char_type>;

  parse_context* parse_ctx_;
  format_context& ctx_;

 public:
  typedef Range range;
  typedef typename base::iterator iterator;
  typedef typename base::format_specs format_specs;

  /**
    \rst
    Constructs an argument formatter object.
    *ctx* is a reference to the formatting context,
    *spec* contains format specifier information for standard argument types.
    \endrst
   */
  arg_formatter(format_context& ctx, parse_context* parse_ctx = nullptr, fmt::format_specs* spec = nullptr)
      : base(Range(ctx.out()), spec, {}), parse_ctx_(parse_ctx), ctx_(ctx) {}

  using base::operator();

  /** Formats an argument of a user-defined type. */
  iterator operator()(typename std::basic_format_arg<format_context>::handle handle) {
    handle.format(*parse_ctx_, ctx_);
    return this->out();
  }

  iterator operator()(monostate) {
    throw format_error("");
  }
};

template <typename Context>
inline fmt::internal::type get_type(basic_format_arg<Context> arg) {
  return visit_format_arg([&] (auto val) {
    using char_type = typename Context::char_type;
    using T = decltype(val);
    if (std::is_same_v<T, monostate>)
      return fmt::internal::none_type;
    if (std::is_same_v<T, bool>)
      return fmt::internal::bool_type;
    if (std::is_same_v<T, char_type>)
      return fmt::internal::char_type;
    if (std::is_same_v<T, int>)
      return fmt::internal::int_type;
    if (std::is_same_v<T, unsigned int>)
      return fmt::internal::uint_type;
    if (std::is_same_v<T, long long int>)
      return fmt::internal::long_long_type;
    if (std::is_same_v<T, unsigned long long int>)
      return fmt::internal::ulong_long_type;
    if (std::is_same_v<T, double>)
      return fmt::internal::double_type;
    if (std::is_same_v<T, long double>)
      return fmt::internal::long_double_type;
    if (std::is_same_v<T, const char_type*>)
      return fmt::internal::cstring_type;
    if (std::is_same_v<T, basic_string_view<char_type>>)
      return fmt::internal::string_type;
    if (std::is_same_v<T, const void*>)
      return fmt::internal::pointer_type;
    assert(get_value(arg).index() == 12);
    return fmt::internal::custom_type;
  }, arg);
}

template <typename Context>
class custom_formatter {
 private:
  using parse_context = basic_format_parse_context<typename Context::char_type>;
  parse_context& parse_ctx_;
  Context& format_ctx_;

 public:
  custom_formatter(parse_context& parse_ctx, Context& ctx) : parse_ctx_(parse_ctx), format_ctx_(ctx) {}

  bool operator()(typename basic_format_arg<Context>::handle h) const {
    h.format(parse_ctx_, format_ctx_);
    return true;
  }

  template <typename T> bool operator()(T) const { return false; }
};

template <typename ArgFormatter, typename Char, typename Context>
struct format_handler : detail::error_handler {
  typedef typename ArgFormatter::range range;

  format_handler(range r, basic_string_view<Char> str,
                 basic_format_args<Context> format_args,
                 fmt::internal::locale_ref loc)
      : parse_ctx(str), context(r.begin(), format_args, loc) {}

  void on_text(const Char* begin, const Char* end) {
    auto size = fmt::internal::to_unsigned(end - begin);
    auto out = context.out();
    auto&& it = fmt::internal::reserve(out, size);
    it = std::copy_n(begin, size, it);
    context.advance_to(out);
  }

  void on_arg_id() {
    arg = context.arg(parse_ctx.next_arg_id());
  }
  void on_arg_id(unsigned id) {
    parse_ctx.check_arg_id(id);
    arg = context.arg(id);
  }
  void on_arg_id(fmt::basic_string_view<Char>) {}

  void on_replacement_field(const Char* p) {
    parse_ctx.advance_to(parse_ctx.begin() + (p - &*parse_ctx.begin()));
    custom_formatter<Context> f(parse_ctx, context);
    if (!visit_format_arg(f, arg))
      context.advance_to(visit_format_arg(ArgFormatter(context, &parse_ctx), arg));
  }

  const Char* on_format_specs(const Char* begin, const Char* end) {
    parse_ctx.advance_to(parse_ctx.begin() + (begin - &*parse_ctx.begin()));
    custom_formatter<Context> f(parse_ctx, context);
    if (visit_format_arg(f, arg)) return &*parse_ctx.begin();
    fmt::basic_format_specs<Char> specs;
    using fmt::internal::specs_handler;
    using parse_context = basic_format_parse_context<Char>;
    fmt::internal::specs_checker<specs_handler<parse_context, Context>> handler(
        specs_handler<parse_context, Context>(specs, parse_ctx, context), get_type(arg));
    begin = parse_format_specs(begin, end, handler);
    if (begin == end || *begin != '}') on_error("missing '}' in format string");
    parse_ctx.advance_to(parse_ctx.begin() + (begin - &*parse_ctx.begin()));
    context.advance_to(visit_format_arg(ArgFormatter(context, &parse_ctx, &specs), arg));
    return begin;
  }

  basic_format_parse_context<Char> parse_ctx;
  Context context;
  basic_format_arg<Context> arg;
};

template <typename T, typename Char>
struct formatter {
  // Parses format specifiers stopping either at the end of the range or at the
  // terminating '}'.
  template <typename ParseContext>
  FMT_CONSTEXPR typename ParseContext::iterator parse(ParseContext& ctx) {
    namespace internal = fmt::internal;
    typedef internal::dynamic_specs_handler<ParseContext> handler_type;
    auto type = internal::mapped_type_constant<T, fmt::buffer_context<Char>>::value;
    internal::specs_checker<handler_type> handler(handler_type(specs_, ctx),
                                                  type);
    auto it = parse_format_specs(ctx.begin(), ctx.end(), handler);
    auto type_spec = specs_.type;
    auto eh = ctx.error_handler();
    switch (type) {
    case internal::none_type:
    case internal::named_arg_type:
      FMT_ASSERT(false, "invalid argument type");
      break;
    case internal::int_type:
    case internal::uint_type:
    case internal::long_long_type:
    case internal::ulong_long_type:
    case internal::bool_type:
      handle_int_type_spec(type_spec,
                           internal::int_type_checker<decltype(eh)>(eh));
      break;
    case internal::char_type:
      handle_char_specs(
          &specs_, internal::char_specs_checker<decltype(eh)>(type_spec, eh));
      break;
    case internal::double_type:
    case internal::long_double_type:
      internal::parse_float_type_spec(specs_, eh);
      break;
    case internal::cstring_type:
      internal::handle_cstring_type_spec(
          type_spec, internal::cstring_type_checker<decltype(eh)>(eh));
      break;
    case internal::string_type:
      internal::check_string_type_spec(type_spec, eh);
      break;
    case internal::pointer_type:
      internal::check_pointer_type_spec(type_spec, eh);
      break;
    case internal::custom_type:
      // Custom format specifiers should be checked in parse functions of
      // formatter specializations.
      break;
    }
    return it;
  }

  template <typename FormatContext>
  auto format(const T& val, FormatContext& ctx) -> decltype(ctx.out()) {
    fmt::internal::handle_dynamic_spec<fmt::internal::width_checker>(
        specs_.width, specs_.width_ref, ctx);
    fmt::internal::handle_dynamic_spec<fmt::internal::precision_checker>(
        specs_.precision, specs_.precision_ref, ctx);
    using range_type = fmt::internal::output_range<typename FormatContext::iterator,
                         typename FormatContext::char_type>;
    return visit_format_arg(arg_formatter<range_type>(ctx, nullptr, &specs_),
                            basic_format_arg<FormatContext>(val));
  }

 private:
  fmt::internal::dynamic_format_specs<Char> specs_;
};
}  // namespace detail

// https://fmt.dev/Text%20Formatting.html#format.functions
template<class... Args>
  string format(string_view fmt, const Args&... args) {
    return vformat(fmt, make_format_args(args...));
  }

template<class... Args>
  wstring format(wstring_view fmt, const Args&... args) {
    return vformat(fmt, make_wformat_args(args...));
  }

string vformat(string_view fmt, format_args args) {
  fmt::memory_buffer mbuf;
  fmt::internal::buffer<char>& buf = mbuf;
  using range = fmt::buffer_range<char>;
  detail::format_handler<detail::arg_formatter<range>, char, format_context>
    h(range(std::back_inserter(buf)), fmt, args, {});
  fmt::internal::parse_format_string<false>(fmt::to_string_view(fmt), h);
  return to_string(mbuf);
}

wstring vformat(wstring_view fmt, wformat_args args);

template<class Out, class... Args>
  Out format_to(Out out, string_view fmt, const Args&... args) {
    using context = basic_format_context<Out, decltype(fmt)::value_type>;
    return vformat_to(out, fmt, {make_format_args<context>(args...)});
  }

template<class Out, class... Args>
  Out format_to(Out out, wstring_view fmt, const Args&... args) {
    using context = basic_format_context<Out, decltype(fmt)::value_type>;
    return vformat_to(out, fmt, {make_format_args<context>(args...)});
  }

template<class Out>
  Out vformat_to(Out out, string_view fmt, format_args_t<Out, char> args) {
    using range = fmt::internal::output_range<Out, char>;
    detail::format_handler<detail::arg_formatter<range>, char, basic_format_context<Out, char>>
      h(range(out), fmt, args, {});
    fmt::internal::parse_format_string<false>(fmt::to_string_view(fmt), h);
    return h.context.out();
  }

template<class Out>
  Out vformat_to(Out out, wstring_view fmt, format_args_t<Out, wchar_t> args);

template<class Out, class... Args>
  format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
                                      string_view fmt, const Args&... args);
template<class Out, class... Args>
  format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,
                                      wstring_view fmt, const Args&... args);

template<class... Args>
  size_t formatted_size(string_view fmt, const Args&... args);
template<class... Args>
  size_t formatted_size(wstring_view fmt, const Args&... args);

#define charT char

template<> struct formatter<charT, charT> : detail::formatter<charT, charT> {};

template<> struct formatter<char, wchar_t>;

template<> struct formatter<charT*, charT> : detail::formatter<const charT*, charT> {};

template<> struct formatter<const charT*, charT> : detail::formatter<const charT*, charT> {};

template<size_t N> struct formatter<const charT[N], charT>
      : detail::formatter<std::basic_string_view<charT>, charT> {};

template<class traits, class Allocator>
  struct formatter<basic_string<charT, traits, Allocator>, charT>
      : detail::formatter<std::basic_string_view<charT>, charT> {};

template<class traits>
  struct formatter<basic_string_view<charT, traits>, charT>
      : detail::formatter<std::basic_string_view<charT>, charT> {};

template <> struct formatter<nullptr_t, charT> : detail::formatter<const void*, charT> {};
template <> struct formatter<void*, charT> : detail::formatter<const void*, charT> {};
template <> struct formatter<const void*, charT> : detail::formatter<const void*, charT> {};
template <> struct formatter<bool, charT> : detail::formatter<bool, charT> {};

template <> struct formatter<signed char, charT> : detail::formatter<int, charT> {};
template <> struct formatter<short, charT> : detail::formatter<int, charT> {};
template <> struct formatter<int, charT> : detail::formatter<int, charT> {};
template <> struct formatter<long, charT>
      : detail::formatter<std::conditional_t<sizeof(long) == sizeof(int), int, long long>, charT> {};
template <> struct formatter<long long, charT> : detail::formatter<long long, charT> {};
template <> struct formatter<unsigned char, charT> : detail::formatter<unsigned int, charT> {};
template <> struct formatter<unsigned short, charT> : detail::formatter<unsigned int, charT> {};
template <> struct formatter<unsigned int, charT> : detail::formatter<unsigned int, charT> {};
template <> struct formatter<unsigned long, charT>
      : detail::formatter<std::conditional_t<sizeof(long) == sizeof(int), unsigned, unsigned long long>, charT> {};
template <> struct formatter<unsigned long long, charT> : detail::formatter<unsigned long long, charT> {};

template <> struct formatter<float, charT> : detail::formatter<double, charT> {};
template <> struct formatter<double, charT> : detail::formatter<double, charT> {};
template <> struct formatter<long double, charT> : detail::formatter<long double, charT> {};

#undef charT

#define charT wchar_t

template<> struct formatter<charT, charT> : detail::formatter<charT, charT> {};

template<> struct formatter<char, wchar_t> : detail::formatter<charT, charT> {};

template<> struct formatter<charT*, charT> : detail::formatter<const charT*, charT> {};

template<> struct formatter<const charT*, charT> : detail::formatter<const charT*, charT> {};

template<size_t N> struct formatter<const charT[N], charT>
      : detail::formatter<std::basic_string_view<charT>, charT> {};

template<class traits, class Allocator>
  struct formatter<std::basic_string<charT, traits, Allocator>, charT>
      : detail::formatter<std::basic_string_view<charT>, charT> {};

template<class traits>
  struct formatter<std::basic_string_view<charT, traits>, charT>
      : detail::formatter<std::basic_string_view<charT>, charT> {};

template <> struct formatter<nullptr_t, charT> : detail::formatter<const void*, charT> {};
template <> struct formatter<void*, charT> : detail::formatter<const void*, charT> {};
template <> struct formatter<const void*, charT> : detail::formatter<const void*, charT> {};
template <> struct formatter<bool, charT> : detail::formatter<bool, charT> {};

template <> struct formatter<signed char, charT> : detail::formatter<int, charT> {};
template <> struct formatter<short, charT> : detail::formatter<int, charT> {};
template <> struct formatter<int, charT> : detail::formatter<int, charT> {};
template <> struct formatter<long, charT>
      : detail::formatter<std::conditional_t<sizeof(long) == sizeof(int), int, long long>, charT> {};
template <> struct formatter<long long, charT> : detail::formatter<long long, charT> {};
template <> struct formatter<unsigned char, charT> : detail::formatter<unsigned int, charT> {};
template <> struct formatter<unsigned short, charT> : detail::formatter<unsigned int, charT> {};
template <> struct formatter<unsigned int, charT> : detail::formatter<unsigned int, charT> {};
template <> struct formatter<unsigned long, charT>
      : detail::formatter<std::conditional_t<sizeof(long) == sizeof(int), unsigned, unsigned long long>, charT> {};
template <> struct formatter<unsigned long long, charT> : detail::formatter<unsigned long long, charT> {};

template <> struct formatter<float, charT> : detail::formatter<double, charT> {};
template <> struct formatter<double, charT> : detail::formatter<double, charT> {};
template <> struct formatter<long double, charT> : detail::formatter<long double, charT> {};

#undef charT

  template<> struct formatter<const wchar_t, char> {
    formatter() = delete;
  };
}

#endif  // FMT_FORMAT_