将概念映射到具体类型的惯用方法

Question

给定一组C++概念：

concept A = ...;
concept B = ...;
concept C = ...;

class ProcessA;
class ProcessB;
class ProcessC;

std::is_same_v<get_matching_type<TypeThatSatisfiesA>, ProcessA>;
std::is_same_v<get_matching_type<TypeThatSatisfiesB>, ProcessB>;
std::is_same_v<get_matching_type<TypeThatSatisfiesC>, ProcessC>;

 using get_matching_type = std::conditional_t<A<T>, ProcessA, 
                              std::conditional_t<B<T>, ProcessB, 
                                std::conditional_t<C<T>, ProcessC>
                              >
                            >; 

template<A T>
struct get_matching_type<T> { using type = ProcessA; };
template<B T>
struct get_matching_type<T> { using type = ProcessB; };
template<C T>
struct get_matching_type<T> { using type = ProcessC; };

但是样板文件穿过屋顶：）

Answer 1

“模式匹配”可以通过重载完成：

template <TypeThatSatisfiesA T> ProcessA helper(T*);
template <TypeThatSatisfiesB T> ProcessB helper(T*);
template <TypeThatSatisfiesC T> ProcessC helper(T*);

template <typename T>
using get_matching_type = decltype(helper(std::declval<T*>()));

演示