The concept is not checked in the procedure body during the declaration, like a
regular non generic type would be. That's unfortunate. I wonder if there's a
conservative solution to rule out cases like this without making the concepts
unusable?
For those who use C++, C++ 20 concepts fail this test as well
++
#include <iostream>
#include <string>
#include <cstddef>
#include <concepts>
template<typename T>
concept Aclass = requires(T a) {
{ a.inum } -> std::convertible_to<int>;
};
struct Anobj {
Anobj(float fnum, int inum) { this->fnum = fnum; this->inum = inum; }
float fnum;
int inum;
};
struct Bnobj {
Bnobj(std::string text, int inum) { this->text = text; this->inum = inum;
}
std::string text;
int inum;
};
struct Cnobj {
Cnobj(std::string text, int jnum) { this->text = text; this->jnum = jnum;
}
std::string text;
int jnum;
};
template<Aclass T>
void cdemookay(T a) {
std::cout << a.inum << '\n';
}
template<Aclass T>
void cdemowrong(T a) {
std::cout << a.text << '\n';
}
/* The compiler rejects this
void cdemowrong(Anobj a) {
std::cout << a.text << '\n';
}
*/
int main() {
auto p = Anobj(3.33, 7);
auto q = Bnobj("empty", 5);
auto r = Cnobj("empty", 12);
cdemookay(p);
cdemookay(q);
cdemowrong(q);
}
Run
