First try:
class Local {
public:
Local() {std::cout << "default\n"; }
Local(const Local&) {std::cout << "copy ctor!\n"; }
};
int main() {
// Direct list init -> Value init -> Default init
Local obj{};
// Copy initialization -> non-explicit copy ctor
Local obj_one = obj;
// Temporary value init -> Copy initialization -> non-explicit copy ctor
Local obj_two = Local{};
return 0;
}
Second try (add explicit):
class Local {
public:
Local() {std::cout << "default\n"; }
// now here explicit
explicit Local(const Local&) {std::cout << "copy ctor!\n"; }
};
int main() {
Local obj{};
// (1) Error, copy-initialization does not consider explicit constructor
Local obj_one = obj;
// (2) Why there is no error?
Local obj_two = Local{};
return 0;
}
In case (1) everything - fine. But what about case (2)? I read in this post that in case (2):
Value-initializes a temporary and then copies that value into c2 (Read 5.2.3/2 and 8.6/14). This of course will require a non-explicit copy constructor (Read 8.6/14 and 12.3.1/3 and 13.3.1.3/1 ).
clang++ -std=c++17 main.cpp
