Hi,
Motivation:
Currently for class T following declarations have different initialization rules depending on whether some constructors are declared explicit or not.
T a{b}; // 1
T a = {b}; // 2
T a = b; // 3
But since C++17 guaranteed copy-ellision this divergence doesn't really make sense. In all scenarios the initialized object is always of type T, and we are explicit about it because we provide the type in the declaration.
So there is no possibility of unintended conversion that 'explicit' keyword is supposed to protect from.
My proposal is:
- in C++29 add a warning for scenarios 2) and 3) if they would select a different constructor than 1),
- in C++32 make 2) and 3) behave exactly the same as 1).
Regards,
Maciej Cencora