Okay, that makes a kind of sense.

Would the thing to do be to submit a proposal to update the relevant
optional functions, then?


On Fri, Sep 25, 2020 at 4:51 AM Maciej Cencora <m.cencora_at_[hidden]> wrote:

> ... 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
>>>
>>