LWG-3870 Remove `voidify`

[StephanTLavavej]

LWG-3870 Remove voidify

[frederick-vs-ja]

WOW! Since operator=, swap, and emplace of expected are specified with construct_at ([expected.expected]), they are now completely broken for a const or volatile value_type.

[CaseyCarter]

WOW! Since operator=, swap, and emplace of expected are specified with construct_at ([expected.expected]), they are now completely broken for a const or volatile value_type.

A. Jiang (@frederick-vs-ja) Have you reported this to LWG?

[frederick-vs-ja]

WOW! Since operator=, swap, and emplace of expected are specified with construct_at ([expected.expected]), they are now completely broken for a const or volatile value_type.

A. Jiang (@frederick-vs-ja) Have you reported this to LWG?

No, I haven't. I'm not sure how to fix swap...

Now I've sent a mail and proposed a resolution

• store the member as remove_cv_t<T>;
• during construction/destruction, or backup by move construction in operator=/swap, it is accessed via cv-unqualified lvalues,
• otherwise, it is accessed as a possibly cv-qualified glvalue, respecting the cv-qualification on T.