How to create a concept to check if all the given type parameters are different in C++?

Question

A concept which checks if the first given type parameter is different from the rest of type parameters is as following:

template<typename TYPE, typename ... TYPES>
concept different = ((not std::same_as<TYPE, TYPES>) and ...);

(std::same_as is from <concepts> standard library)

But how to check if all the given type parameters are different from each other?

Answer 1

This an example of the concept you can use :

#include <type_traits>

template<typename arg_t, typename... args_t>
static consteval bool all_unique()
{
    if constexpr (sizeof...(args_t) == 0ul)
    {
        return true;
    }
    else
    {
        return (!std::is_same_v<arg_t, args_t> && ...) && all_unique<args_t...>();
    }
}

template<typename... args_t>
concept AllUnique = all_unique<args_t...>();

template<typename...args_t>
void f(args_t... args) requires AllUnique<args_t...>
{

}

int main()
{
    static_assert(all_unique<int>());
    static_assert(all_unique<int,bool>());
    static_assert(!all_unique<int, bool, int>());

    static_assert(AllUnique<int>);
    static_assert(AllUnique<int, bool>);
    static_assert(!AllUnique<int, bool, int>);

    f(1);
    f(1, true);
    // f(1, 2); // indeed does not compile
   
    
    return 0;
}