te')); return $arr; } /* 遍历用户所有主题 * @param $uid 用户ID * @param int $page 页数 * @param int $pagesize 每页记录条数 * @param bool $desc 排序方式 TRUE降序 FALSE升序 * @param string $key 返回的数组用那一列的值作为 key * @param array $col 查询哪些列 */ function thread_tid_find_by_uid($uid, $page = 1, $pagesize = 1000, $desc = TRUE, $key = 'tid', $col = array()) { if (empty($uid)) return array(); $orderby = TRUE == $desc ? -1 : 1; $arr = thread_tid__find($cond = array('uid' => $uid), array('tid' => $orderby), $page, $pagesize, $key, $col); return $arr; } // 遍历栏目下tid 支持数组 $fid = array(1,2,3) function thread_tid_find_by_fid($fid, $page = 1, $pagesize = 1000, $desc = TRUE) { if (empty($fid)) return array(); $orderby = TRUE == $desc ? -1 : 1; $arr = thread_tid__find($cond = array('fid' => $fid), array('tid' => $orderby), $page, $pagesize, 'tid', array('tid', 'verify_date')); return $arr; } function thread_tid_delete($tid) { if (empty($tid)) return FALSE; $r = thread_tid__delete(array('tid' => $tid)); return $r; } function thread_tid_count() { $n = thread_tid__count(); return $n; } // 统计用户主题数 大数量下严谨使用非主键统计 function thread_uid_count($uid) { $n = thread_tid__count(array('uid' => $uid)); return $n; } // 统计栏目主题数 大数量下严谨使用非主键统计 function thread_fid_count($fid) { $n = thread_tid__count(array('fid' => $fid)); return $n; } ?>C++ auto templated function overload ambiguity - Stack Overflow

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    C++ auto templated function overload ambiguity - Stack Overflow

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    #include <iostream>
#include <concepts>


struct Sound { int amplitude; };
struct Light { int brightness; };

template <typename T>
concept Alert = std::derived_from<T, Sound> && std::derived_from<T, Light>;


struct FirstSound : Sound{};
struct FirstLight : Light{};
struct FirstSoundLight : FirstSound, FirstLight{};

struct LastSound : Sound{};
struct LastLight : Light{};
struct LastSoundLight : LastSound, LastLight{};

template <typename T>
concept FirstAlert = std::derived_from<T, FirstSound> && std::derived_from<T, FirstLight>;

template <typename T>
concept LastAlert = std::derived_from<T, LastSound> && std::derived_from<T, LastLight>;


void warn(FirstAlert auto const& a, LastAlert auto const& b)
{ std::cout << "Special warning"; }

void warn(Alert auto const& a, LastAlert auto const& b) = delete;
//{ std::cout << "Deleted warning"; }

void warn(Alert auto const& a, Alert auto const& b)
{ std::cout << "General warning"; }

int main() 
{
    warn(FirstSoundLight{}, LastSoundLight{});
    return 0;
}

    The code above is a simplified version of my problem. How can I make the compiler select functions unambigiously in the given order without explicitly casting the parameters?

    #include <iostream>
#include <concepts>


struct Sound { int amplitude; };
struct Light { int brightness; };

template <typename T>
concept Alert = std::derived_from<T, Sound> && std::derived_from<T, Light>;


struct FirstSound : Sound{};
struct FirstLight : Light{};
struct FirstSoundLight : FirstSound, FirstLight{};

struct LastSound : Sound{};
struct LastLight : Light{};
struct LastSoundLight : LastSound, LastLight{};

template <typename T>
concept FirstAlert = std::derived_from<T, FirstSound> && std::derived_from<T, FirstLight>;

template <typename T>
concept LastAlert = std::derived_from<T, LastSound> && std::derived_from<T, LastLight>;


void warn(FirstAlert auto const& a, LastAlert auto const& b)
{ std::cout << "Special warning"; }

void warn(Alert auto const& a, LastAlert auto const& b) = delete;
//{ std::cout << "Deleted warning"; }

void warn(Alert auto const& a, Alert auto const& b)
{ std::cout << "General warning"; }

int main() 
{
    warn(FirstSoundLight{}, LastSoundLight{});
    return 0;
}

    The code above is a simplified version of my problem. How can I make the compiler select functions unambigiously in the given order without explicitly casting the parameters?

    • c++
    • function
    • c++20
    • auto
    • ambiguity
    Share Improve this question edited Feb 17 at 21:20 Eugene 7,6881 gold badge25 silver badges35 bronze badges asked Feb 17 at 21:02 ahfaktahfakt 435 bronze badges
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    1 Answer 1

    Reset to default 3

    You need to subsume concept Alert in your 2 other concepts:

    template <typename T>
concept FirstAlert = Alert<T> && std::derived_from<T, FirstSound> && std::derived_from<T, FirstLight>;

template <typename T>
concept LastAlert = Alert<T> && std::derived_from<T, LastSound> && std::derived_from<T, LastLight>;

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