args.h

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// Formatting library for C++ - dynamic format arguments
//
// Copyright (c) 2012 - present, Victor Zverovich
// All rights reserved.
//
// For the license information refer to format.h.
 
#ifndef FMT_ARGS_H_
#define FMT_ARGS_H_
 
#include <functional>  // std::reference_wrapper
#include <memory>      // std::unique_ptr
#include <vector>
 
#include "core.h"
 
FMT_BEGIN_NAMESPACE
 
namespace detail {
 
template <typename T> struct is_reference_wrapper : std::false_type {};
template <typename T>
struct is_reference_wrapper<std::reference_wrapper<T>> : std::true_type {};
 
template <typename T> const T& unwrap(const T& v) { return v; }
template <typename T> const T& unwrap(const std::reference_wrapper<T>& v) {
  return static_cast<const T&>(v);
}
 
class dynamic_arg_list {
  // Workaround for clang's -Wweak-vtables. Unlike for regular classes, for
  // templates it doesn't complain about inability to deduce single translation
  // unit for placing vtable. So storage_node_base is made a fake template.
  template <typename = void> struct node {
    virtual ~node() = default;
    std::unique_ptr<node<>> next;
  };
 
  template <typename T> struct typed_node : node<> {
    T value;
 
    template <typename Arg>
    FMT_CONSTEXPR typed_node(const Arg& arg) : value(arg) {}
 
    template <typename Char>
    FMT_CONSTEXPR typed_node(const basic_string_view<Char>& arg)
        : value(arg.data(), arg.size()) {}
  };
 
  std::unique_ptr<node<>> head_;
 
 public:
  template <typename T, typename Arg> const T& push(const Arg& arg) {
    auto new_node = std::unique_ptr<typed_node<T>>(new typed_node<T>(arg));
    auto& value = new_node->value;
    new_node->next = std::move(head_);
    head_ = std::move(new_node);
    return value;
  }
};
}  // namespace detail
 
/**
  \rst
  A dynamic version of `fmt::format_arg_store`.
  It's equipped with a storage to potentially temporary objects which lifetimes
  could be shorter than the format arguments object.
 
  It can be implicitly converted into `~fmt::basic_format_args` for passing
  into type-erased formatting functions such as `~fmt::vformat`.
  \endrst
 */
template <typename Context>
class dynamic_format_arg_store
#if FMT_GCC_VERSION && FMT_GCC_VERSION < 409
    // Workaround a GCC template argument substitution bug.
    : public basic_format_args<Context>
#endif
{
 private:
  using char_type = typename Context::char_type;
 
  template <typename T> struct need_copy {
    static constexpr detail::type mapped_type =
        detail::mapped_type_constant<T, Context>::value;
 
    enum {
      value = !(detail::is_reference_wrapper<T>::value ||
                std::is_same<T, basic_string_view<char_type>>::value ||
                std::is_same<T, detail::std_string_view<char_type>>::value ||
                (mapped_type != detail::type::cstring_type &&
                 mapped_type != detail::type::string_type &&
                 mapped_type != detail::type::custom_type))
    };
  };
 
  template <typename T>
  using stored_type = conditional_t<
      std::is_convertible<T, std::basic_string<char_type>>::value &&
          !detail::is_reference_wrapper<T>::value,
      std::basic_string<char_type>, T>;
 
  // Storage of basic_format_arg must be contiguous.
  std::vector<basic_format_arg<Context>> data_;
  std::vector<detail::named_arg_info<char_type>> named_info_;
 
  // Storage of arguments not fitting into basic_format_arg must grow
  // without relocation because items in data_ refer to it.
  detail::dynamic_arg_list dynamic_args_;
 
  friend class basic_format_args<Context>;
 
  unsigned long long get_types() const {
    return detail::is_unpacked_bit | data_.size() |
           (named_info_.empty()
                ? 0ULL
                : static_cast<unsigned long long>(detail::has_named_args_bit));
  }
 
  const basic_format_arg<Context>* data() const {
    return named_info_.empty() ? data_.data() : data_.data() + 1;
  }
 
  template <typename T> void emplace_arg(const T& arg) {
    data_.emplace_back(detail::make_arg<Context>(arg));
  }
 
  template <typename T>
  void emplace_arg(const detail::named_arg<char_type, T>& arg) {
    if (named_info_.empty()) {
      constexpr const detail::named_arg_info<char_type>* zero_ptr{nullptr};
      data_.insert(data_.begin(), {zero_ptr, 0});
    }
    data_.emplace_back(detail::make_arg<Context>(detail::unwrap(arg.value)));
    auto pop_one = [](std::vector<basic_format_arg<Context>>* data) {
      data->pop_back();
    };
    std::unique_ptr<std::vector<basic_format_arg<Context>>, decltype(pop_one)>
        guard{&data_, pop_one};
    named_info_.push_back({arg.name, static_cast<int>(data_.size() - 2u)});
    data_[0].value_.named_args = {named_info_.data(), named_info_.size()};
    guard.release();
  }
 
 public:
  constexpr dynamic_format_arg_store() = default;
 
  /**
    \rst
    Adds an argument into the dynamic store for later passing to a formatting
    function.
 
    Note that custom types and string types (but not string views) are copied
    into the store dynamically allocating memory if necessary.
 
    **Example**::
 
      fmt::dynamic_format_arg_store<fmt::format_context> store;
      store.push_back(42);
      store.push_back("abc");
      store.push_back(1.5f);
      std::string result = fmt::vformat("{} and {} and {}", store);
    \endrst
  */
  template <typename T> void push_back(const T& arg) {
    if (detail::const_check(need_copy<T>::value))
      emplace_arg(dynamic_args_.push<stored_type<T>>(arg));
    else
      emplace_arg(detail::unwrap(arg));
  }
 
  /**
    \rst
    Adds a reference to the argument into the dynamic store for later passing to
    a formatting function.
 
    **Example**::
 
      fmt::dynamic_format_arg_store<fmt::format_context> store;
      char band[] = "Rolling Stones";
      store.push_back(std::cref(band));
      band[9] = 'c'; // Changing str affects the output.
      std::string result = fmt::vformat("{}", store);
      // result == "Rolling Scones"
    \endrst
  */
  template <typename T> void push_back(std::reference_wrapper<T> arg) {
    static_assert(
        need_copy<T>::value,
        "objects of built-in types and string views are always copied");
    emplace_arg(arg.get());
  }
 
  /**
    Adds named argument into the dynamic store for later passing to a formatting
    function. ``std::reference_wrapper`` is supported to avoid copying of the
    argument. The name is always copied into the store.
  */
  template <typename T>
  void push_back(const detail::named_arg<char_type, T>& arg) {
    const char_type* arg_name =
        dynamic_args_.push<std::basic_string<char_type>>(arg.name).c_str();
    if (detail::const_check(need_copy<T>::value)) {
      emplace_arg(
          fmt::arg(arg_name, dynamic_args_.push<stored_type<T>>(arg.value)));
    } else {
      emplace_arg(fmt::arg(arg_name, arg.value));
    }
  }
 
  /** Erase all elements from the store */
  void clear() {
    data_.clear();
    named_info_.clear();
    dynamic_args_ = detail::dynamic_arg_list();
  }
 
  /**
    \rst
    Reserves space to store at least *new_cap* arguments including
    *new_cap_named* named arguments.
    \endrst
  */
  void reserve(size_t new_cap, size_t new_cap_named) {
    FMT_ASSERT(new_cap >= new_cap_named,
               "Set of arguments includes set of named arguments");
    data_.reserve(new_cap);
    named_info_.reserve(new_cap_named);
  }
};
 
FMT_END_NAMESPACE
 
#endif  // FMT_ARGS_H_