C++20: concept definition parameters seems inverted

[JUANDENT]

Hi,

This next concept:

template <class T, class U>
concept SubClass = std::is_base_of<U, T>::value;

used in this context:

template<SubClass<ABase> X>
void f(X);  // X is constrained by SubClass<X, ABase> 

seems inverted to me: the first template argument to SubClass should correspond to the template parameter T in which case X is constrained by SubClass<ABase,X>.
in other words by std::is_base_of<X, ABase>::value
yet the 1ste argument to is_base_of is supposed to be the base class, the second the derived class

see my point?

[Cubbi]

Looks like that "SubClass" was someone's version of the standard library concept std::derived_from https://en.cppreference.com/w/cpp/concepts/derived_from

in any case, it works here as intended.

The syntax template<SubClass<ABase> X> is short for template<class X> requires SubClass<X, ABase>
you can find that on cppreference https://en.cppreference.com/w/cpp/language/template_parameters#Type_template_parameter - it even has an example
template<C3<int> T> struct s4; // constraint-expression is C3<T, int>