learn_class/modern_cpp_30/constexpr/output_container.h - master - githubmirror/CPlusPlusThings

learn_class/modern_cpp_30/constexpr/output_container.h
134 строки4 KB
zhangxing
support bazel complie this project and format code.
30 мар 2024, 17:00
30 мар 2024, 17:003c8a3f2
//
// Created by light on 20-1-8.
//

#ifndef MORDEN_C_OUTPUT_CONTAINER_H
#define MORDEN_C_OUTPUT_CONTAINER_H

#include <ostream>     // std::ostream
#include <type_traits> // std::false_type/true_type/decay_t/is_same_v
#include <utility>     // std::declval/pair

// 检测是否是pair
template <typename T> struct is_pair : std::false_type {};
template <typename T, typename U>
struct is_pair<std::pair<T, U>> : std::true_type {};
template <typename T> inline constexpr bool is_pair_v = is_pair<T>::value;

// 检测是否可以直接输出
template <typename T> struct has_output_function {
  template <class U>
  static auto output(U *ptr)
      -> decltype(std::declval<std::ostream &>() << *ptr, std::true_type());

  template <class U> static std::false_type output(...);

  static constexpr bool value = decltype(output<T>(nullptr))::value;
};

template <typename T>
inline constexpr bool has_output_function_v = has_output_function<T>::value;

enum CHARS {
  ORD,   // 其他类型
  CHAR,  // char 类型
  STRING // string 类型
};

template <typename T> int ischarOrString(T &elem) {
  using std::decay_t;
  using std::is_same_v;
  using element_type = decay_t<decltype(elem)>;
  constexpr bool is_char_v = is_same_v<element_type, char>;
  constexpr bool is_string_v = is_same_v<element_type, char *> ||
                               is_same_v<element_type, const char *> ||
                               is_same_v<element_type, std::string>;
  if (is_char_v)
    return CHAR;
  else if (is_string_v)
    return STRING;
  else
    return ORD;
}

template <typename T> void output(T &elem, int type, std::ostream &os) {
  switch (type) {
  case CHAR:
    os << '\'' << elem << '\'';
    break;
  case STRING:
    os << '\"' << elem << '\"';
    break;
  case ORD:
    os << elem;
    break;
  }
}

template <typename T, typename Cont>
auto output_element(std::ostream &os, const T &element, const Cont &) ->
    typename std::enable_if<is_pair<typename Cont::value_type>::value,
                            bool>::type {
  int ftype = ischarOrString(element.first);
  int stype = ischarOrString(element.second);

  output(element.first, ftype, os);
  os << " => ";
  output(element.second, stype, os);
  return true;
}

template <typename T, typename Cont>
auto output_element(std::ostream &os, const T &element, const Cont &) ->
    typename std::enable_if<!is_pair<typename Cont::value_type>::value,
                            bool>::type {
  int etype = ischarOrString(element);
  output(element, etype, os);
  return false;
}

template <typename T, typename U>
std::ostream &operator<<(std::ostream &os, const std::pair<T, U> &pr) {
  os << '(' << pr.first << ", " << pr.second << ')';
  return os;
}

// template<typename T, typename Cont>
// auto output_element(std::ostream& os, const T& element,
//                     const Cont&, const std::true_type)
//-> decltype(std::declval<typename Cont::key_type>(), os)
//{
//     os << element.first << " => " << element.second;
//     return os;
// }
//
// template <typename T, typename Cont>
// auto output_element(std::ostream& os, const T& element,
//                     const Cont&, ...)
//-> decltype(os)
//{
//     os << element;
//     return os;
// }

// 针对没有输出函数的容器处理
template <typename T, typename = std::enable_if_t<!has_output_function_v<T>>>
auto operator<<(std::ostream &os, const T &container)
    -> decltype(container.begin(), container.end(), os) {
  os << "{ ";
  if (!container.empty()) {
    bool on_first_element = true;
    for (auto elem : container) {
      if (!on_first_element) {
        os << ", ";
      } else {
        on_first_element = false;
      }
      output_element(os, elem, container);
    }
  }
  os << " }";
  return os;
}

#endif // MORDEN_C_OUTPUT_CONTAINER_H