Probably, what I was thinking is "where would be the point of instantiation of the attribute" ?

Sorry, I forgot to split the sentences, "Probably" is refering to Corentin answer and after that is my question.

2 - constexpr auto y = std::meta::attribute<Y&>(reflexpr(W)) // can I get a reference to Y ? could it be copy free ?

I mean const ref

2 - constexpr auto y = std::meta::attribute<const Y&>(reflexpr(W)) // can I get a const reference to Y ? could it be copy free ?

Cleiton