Corentin, you wrote a paper on this topic, n'est ce pas?

On Tue, 10 Nov 2020 at 15:22, Cleiton Santoia via SG7 <> wrote:
namespace std::meta { 
  template consteval <typename Attr>   // Need to be a template ?
  bool has_attribute(info x);

  template consteval <typename Attr> //  template parameter only in result ?
  Attr attribute(info x);              


public X {};
public Y { Y(int) {} };

struct V {};
struct W {};

constexpr auto x = std::meta::attribute<X>(reflexpr(V));  // ok x = X();
constexpr auto y = std::meta::attribute<Y>(reflexpr(W));  // ok y = Y(10);

but what if you ask for  

constexpr auto y2 = std::meta::attribute<Y>(reflexpr(V));  ??? 

since Y cannot be default initialized ?

Program is il-formed

I believe std::meta::attribute should a plural filtered funcion

template consteval 
std::vector<info> attributes_of( info class_type, Args ...filters );  

How do you get a value out of the attribute ?


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