C++ currently has no way to create a named and reusable set of types that
can be used as a concept constraint. Every time you write a concept
constraint or requires section, you must enumerate the types, which makes
large constraints unreadable and unmaintainable.

I propose a solution, a type with template arguments for any type,
including user-defined types and standard library types, which you can then
use when creating a concept or requires section, by stating the named type
list and the type you want to check.

Here is how my implementation works:

template<typename T>
 requires std::is_same_v<T, unsigned char> || std::is_same_v<T,
unsigned short> || std::is_same_v<T, unsigned int> ||
std::is_same_v<T, unsigned long> || std::is_same_v<T, unsigned long
long>void natural_only(T);template<typename T>
 requires std::is_same_v<T, unsigned char> || std::is_same_v<T,
unsigned short> || std::is_same_v<T, unsigned int> ||
std::is_same_v<T, unsigned long> || std::is_same_v<T, unsigned long
long> || std::is_same_v<T, char> || std::is_same_v<T, short> ||
std::is_same_v<T, int> || std::is_same_v<T, long> || std::is_same_v<T,
long long>void whole_only(T);
using natural_numbers = typename tag::merge_tags_and_types<unsigned
char, unsigned short, unsigned int, unsigned long, unsigned long
long>::type;using whole_numbers = typename
tag::merge_tags_and_types<signed char, short, int, long, long long,
natural_numbers>::type;using real_numbers = typename
tag::merge_tags_and_types<float, double, long double>::type;using
numbers = typename tag::merge_tags_and_types<whole_numbers,
real_numbers>::type;
template<typename T>concept is_number = tag::contains<numbers, T>;
template<typename T>concept is_whole = tag::contains<whole_numbers, T>;
template<typename T>concept is_natural = tag::contains<natural_numbers, T>;
template<typename T>concept is_real = tag::contains<real_numbers, T>;
template<typename T>
 requires tag::contains<natural_numbers, T>void natural_only(T);

You can read the source of the implementation at Github
<https://github.com/progress-3325/tagging>. A paper draft is forthcoming

I am looking for feedback before submitting a formal paper.