std::common_comparison_category
From cppreference.com
Defined in header <compare>


template<class... Ts> struct common_comparison_category { 
(since C++20)  
The class template std::common_comparison_category
provides an alias (as the member typedef type
) for the strongest comparison category to which all of the template arguments Ts...
can be converted.
In detail, the common comparison type of a list of n types T0...Tn1 is defined as follows:
 If any Ti is not a comparison category type (std::weak_equality, std::strong_equality, std::partial_ordering, std::weak_ordering, std::strong_ordering), U is void.
 Otherwise, if at least one Ti is std::weak_equality or at least one Ti is std::strong_equality and at least one Ti is std::partial_ordering or std::weak_ordering, U is std::weak_equality
 Otherwise, if at least one Ti is std::strong_equality, U is std::strong_equality
 Otherwise, (if there is no std::weak_equality and no std::strong_equality) if at least one Ti is std::partial_ordering, U is std::partial_ordering
 Otherwise, if at least one Ti is std::weak_ordering, U is std::weak_ordering
 Otherwise (if every Ti is std::strong_ordering, or if the list is empty), U is std::strong_ordering.
Template parameters
...Ts    a possibly empty list of types 
Helper template
template< class... Ts > using common_comparison_category_t = typename common_comparison_category<Ts...>::type; 
(since C++20)  
Member types
Member type  Definition 
type

the strongest common comparison category (as defined above) 
Example
This section is incomplete Reason: no example 
See also
(C++20) 
the result type of 3way comparison that supports all 6 operators and is substitutable (class) 
(C++20) 
the result type of 3way comparison that supports all 6 operators and is not substitutable (class) 
(C++20) 
the result type of 3way comparison that supports all 6 operators, is not substitutable, and allows incomparable values (class) 
(C++20) 
the result type of 3way comparison that supports only equality/inequality and is substitutable (class) 
(C++20) 
the result type of 3way comparison that supports only equality/inequality and is not substitutable (class) 