On 7/21/24 18:51, Frederick Virchanza Gotham via Std-Proposals wrote:

> We can use "__datasizeof" or "[[no_unique_address]]" in order to try
> use the tail padding of T to store the boolean, and if we succeed,
> then sizeof(optional<T>) == sizeof(T).

This sounds like an implementation detail.

> If T has no tail padding, then we need an extra byte to store the
> boolean. Unless . . . we had the ability to mark the class
> 'null_bytes==null_object" as follows:

Optionals that leverage unused values / bit-patterns to mark the object
as disengaged has existed for a long time:

   https://github.com/akrzemi1/markable

You need, as usual, to provide the motivation for adding this to the
standard.