135 lines
4.8 KiB
C++
135 lines
4.8 KiB
C++
/*
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* Written by Wu Yongwei <wuyongwei AT gmail DOT com>.
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*
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* Using this file requires a C++17-compliant compiler.
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*
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* This is free and unencumbered software released into the public domain.
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*
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* Anyone is free to copy, modify, publish, use, compile, sell, or
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* distribute this software, either in source code form or as a compiled
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* binary, for any purpose, commercial or non-commercial, and by any
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* means.
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*
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* In jurisdictions that recognize copyright laws, the author or authors
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* of this software dedicate any and all copyright interest in the
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* software to the public domain. We make this dedication for the benefit
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* of the public at large and to the detriment of our heirs and
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* successors. We intend this dedication to be an overt act of
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* relinquishment in perpetuity of all present and future rights to this
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* software under copyright law.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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* IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
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* OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
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* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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* OTHER DEALINGS IN THE SOFTWARE.
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*
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* For more information, please refer to <http://unlicense.org>
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*
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*/
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#ifndef OUTPUT_CONTAINER_H
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#define OUTPUT_CONTAINER_H
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#include <ostream> // std::ostream
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#include <type_traits> // std::false_type/true_type/decay_t/is_same_v
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#include <utility> // std::declval/pair
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// Type trait to detect std::pair
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template <typename T> struct is_pair : std::false_type {};
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template <typename T, typename U>
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struct is_pair<std::pair<T, U>> : std::true_type {};
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template <typename T> inline constexpr bool is_pair_v = is_pair<T>::value;
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// Type trait to detect whether an output function already exists
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template <typename T> struct has_output_function {
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template <class U>
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static auto output(U *ptr)
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-> decltype(std::declval<std::ostream &>() << *ptr, std::true_type());
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template <class U> static std::false_type output(...);
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static constexpr bool value = decltype(output<T>(nullptr))::value;
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};
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template <typename T>
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inline constexpr bool has_output_function_v = has_output_function<T>::value;
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/* NB: Visual Studio 2017 (or below) may have problems with
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* has_output_function_v<T>: you should then use
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* has_output_function<T>::value instead, or upgrade to
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* Visual Studio 2019. */
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// Output function for std::pair
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template <typename T, typename U>
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std::ostream &operator<<(std::ostream &os, const std::pair<T, U> &pr);
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// Element output function for containers that define a key_type and
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// have its value type as std::pair
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template <typename T, typename Cont>
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auto output_element(std::ostream &os, const T &element, const Cont &,
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const std::true_type)
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-> decltype(std::declval<typename Cont::key_type>(), os);
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// Element output function for other containers
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template <typename T, typename Cont>
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auto output_element(std::ostream &os, const T &element, const Cont &, ...)
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-> decltype(os);
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// Main output function, enabled only if no output function already exists
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template <typename T, typename = std::enable_if_t<!has_output_function_v<T>>>
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auto operator<<(std::ostream &os, const T &container)
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-> decltype(container.begin(), container.end(), os) {
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using std::decay_t;
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using std::is_same_v;
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using element_type = decay_t<decltype(*container.begin())>;
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constexpr bool is_char_v = is_same_v<element_type, char>;
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if constexpr (!is_char_v) {
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os << "{ ";
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}
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if (!container.empty()) {
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auto end = container.end();
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bool on_first_element = true;
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for (auto it = container.begin(); it != end; ++it) {
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if constexpr (is_char_v) {
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if (*it == '\0') {
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break;
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}
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}
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if constexpr (!is_char_v) {
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if (!on_first_element) {
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os << ", ";
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} else {
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on_first_element = false;
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}
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}
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output_element(os, *it, container, is_pair<element_type>());
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}
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}
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if constexpr (!is_char_v) {
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os << " }";
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}
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return os;
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}
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template <typename T, typename Cont>
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auto output_element(std::ostream &os, const T &element, const Cont &,
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const std::true_type)
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-> decltype(std::declval<typename Cont::key_type>(), os) {
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os << element.first << " => " << element.second;
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return os;
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}
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template <typename T, typename Cont>
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auto output_element(std::ostream &os, const T &element, const Cont &, ...)
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-> decltype(os) {
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os << element;
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return os;
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}
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template <typename T, typename U>
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std::ostream &operator<<(std::ostream &os, const std::pair<T, U> &pr) {
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os << '(' << pr.first << ", " << pr.second << ')';
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return os;
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}
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#endif // OUTPUT_CONTAINER_H
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