c++11 - C++ how to generate all the permutations of function overloads? -


lets have classes date , classes year, month , day.

struct date {   date(year year, month month, day day) : d(day), m(month), y(year) {};   date(month month, day day, year year) : d(day), m(month), y(year) {};   date(day day, month month, year year) : d(day), m(month), y(year) {};   date(day day, year year, month month) : d(day), m(month), y(year) {};   ...   ...    private:     day d;     month m;     year y; }

this allows me not have specific layout of arguments date have lot of overloadings.

am able generate permutations/overloadings automatically?

just clear:

  • permutations of argument layout, nothing them should change know not possible automate.
  • all generated overloadings should have same code layout of arguments changes not logic itself.

with c++14, may do:

struct date { public:     date(const year& year, const month& month, const day& day) :         d(day), m(month), y(year)     {}      template <typename t1, typename t2, typename t3>     date(const t1& t1, const t2& t2, const t3& t3) :          date(std::get<year>(std::tie(t1, t2, t3)),              std::get<month>(std::tie(t1, t2, t3)),              std::get<day>(std::tie(t1, t2, t3)))     {}  private:     day d;     month m;     year y; };

edit: if allow default argument, may like:

namespace detail {     template <typename t, typename... ts> struct has_t;      template <typename t> struct has_t<t> : std::false_type {};      template <typename t, typename... ts> struct has_t<t, t, ts...>     : std::true_type {};      template <typename t, typename tail, typename... ts>     struct has_t<t, tail, ts...> : has_t<t, ts...> {};      template <typename t, typename... ts>     const t& get_or_default_impl(std::true_type,                                  const std::tuple<ts...>& t,                                  const t&)     {         return std::get<t>(t);     }      template <typename t, typename... ts>     const t& get_or_default_impl(std::false_type,                                  const std::tuple<ts...>&,                                  const t& default_value)     {         return default_value;     }      template <typename t1, typename t2> struct is_included;      template <typename... ts>     struct is_included<std::tuple<>, std::tuple<ts...>> : std::true_type {};      template <typename t, typename... ts, typename ... ts2>     struct is_included<std::tuple<t, ts...>, std::tuple<ts2...>> :         std::conditional_t<has_t<t, ts2...>::value,                           is_included<std::tuple<ts...>, std::tuple<ts2...>>,                           std::false_type> {};  }  template <typename t, typename... ts> const t& get_or_default(const std::tuple<ts...>& t,                         const t& default_value = t{}) {     return detail::get_or_default_impl<t>(detail::has_t<t, ts...>{}, t, default_value); }

and then

struct date { public:     date(const year& year, const month& month, const day& day) :         d(day), m(month), y(year)     {}      template <typename ... ts,               typename std::enable_if_t<                   detail::is_included<std::tuple<ts...>,                   std::tuple<year, month, day>>::value>* = nullptr>     date(const ts&... ts) :         date(get_or_default<const year&>(std::tie(ts...)),              get_or_default<const month&>(std::tie(ts...)),              get_or_default<const day&>(std::tie(ts...)))     {}  private:     day d;     month m;     year y; };

live demo
live demo invalid constructor call


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