... was updated to allow changing active union member **in constexpr
context** (P1330).

pt., 25 wrz 2020 o 13:49 Maciej Cencora <m.cencora_at_[hidden]> napisał(a):

> It is not an oversight. It's just nobody has proposed updates in the
> standard library after C++20 language was updated to allow changing active
> union member (P1330).
>
> Regards,
> Maciej
>
>
> czw., 24 wrz 2020 o 10:13 Michael Scire via Std-Proposals <
> std-proposals_at_[hidden]> napisał(a):
>
>> The rules surrounding constexpr for std::optional seem inconsistent --
>> like there are a lot of functions that are "just" missing the keyword due
>> to oversight.
>>
>> For example, `optional(std::nullopt_t)` is constexpr, but `optional
>> &operator=(std::nullopt_t)` is not.
>>
>> This leads to the following (https://godbolt.org/z/8a9Ga3):
>>
>> // Okay
>> ```
>> constexpr std::optional<int> ValidOptional = []{
>> std::optional<int> opt(std::nullopt);
>> opt = std::optional<int>(std::nullopt);
>> return opt;
>> }();
>> ```
>>
>> // Compiler error
>> ```
>> constexpr std::optional<int> InvalidOptional = []{
>> std::optional<int> opt(std::nullopt);
>> opt = std::nullopt;
>> return opt;
>> }();
>> ```
>>
>> Other oversights:
>> `template<typename U> optional(U &&)` is constexpr, but
>> `template<typename U> optional &operator=(U &&)` is not.
>>
>> Things that are less obviously oversights, but might want to change:
>> `emplace` is not constexpr, even though the constructors it would call
>> are.
>> `reset` is not constexpr.
>> `swap(optional &)` is not constexpr, nor is std::swap for optionals.
>> (std::swap is constexpr for other types).
>> copy constructor/move constructor for template<typename T> optional<U>
>> are not constexpr, even though optional(U &&) is.
>> If the following changed, copy/move assignment operators would probably
>> also want to be constexpr.
>>
>> --
>> Std-Proposals mailing list
>> Std-Proposals_at_[hidden]
>> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals
>>
>