C ++如何生成函数重载的所有排列? [英] C++ how to generate all the permutations of function overloads?
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问题描述
假设我有类日期
和类年
,月
和日
。
struct Date {
日期(年年,月月,日):d(日),m(月),y(年){};
日期(月份,日期,年份):d(日期),m(月份),y(年份){};
日期(日期,月份,年份):d(日期),m(月份),y(年份){};
日期(日期,年份,月份):d(日期),m(月份),y(年份){};
...
...
私人:
第d天;
月m;
年y;
}
这使我不能有<$ c $
strong>只是为了清楚起见:
- 所有生成的重载都应该有相同的代码,只有
布局
使用C ++ 14,你可以这样做:
struct Date {
public:
Date(const Year& year,const Month& month,const日期&日):
d(日),m(月),y(年)
{}
模板< 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> b $ b {}
private:
Day d;
月m;
年y;
};
编辑:
如果您还允许使用默认参数,您可以执行类似以下操作:
命名空间详细信息
{
template< typename T,typename .. 。 struct has_T;
template< typename T> struct has_T< T> :std :: false_type {};
template< typename T,typename ... Ts> struct has_T :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&
}
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& T,Ts ...> {},t,default_value);
}
然后
struct Date {
public:
Date(const Year& year,const Month& month,const Day& day):
d (month),y(year)
{}
template< typename ... Ts,typename std :: enable_if_t< detail :: is_included< std :: tuple& 。>,std :: tuple< Year,Month,Day>> :: value> * = nullptr>
Date(const Ts& ... ts):
Date(get_or_default< const Year&>(std :: tie(ts ...)),
get_or_default& >(std :: tie(ts ...)),
get_or_default< const Day&>(std :: tie(ts ...)))
{}
b $ b private:
Day d;
月m;
年y;
};
Lets say I have classes Date
and classes Year
, Month
and 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 to have a specific layout of arguments for Date
as I have a lot of overloadings.
Am I able to generate all the permutations/overloadings automatically?
Just to be clear:
- Permutations are only of argument layout, nothing about them should change as I know that would not be possible to automate.
- All the generated overloadings should have the same code as only the layout of arguments changes not the logic itself.
解决方案
With C++14, you 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 you would also allow default argument, you may do something 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 with invalid constructor call
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