Is it too late to ask for a std::optional change?
Le ven. 14 déc. 2018 à 13:37, Chris Dumez <cdu...@apple.com> a écrit :
>
> Hi,
>
> I have now been caught twice by std::optional’s move constructor. It turns
> out that it leaves the std::optional being moved-out *engaged*, it merely
> moves its value.
>
> For example, testOptional.cpp:
> #include <iostream>
> #include <optional>
>
> int main()
> {
> std::optional<int> a = 1;
> std::optional<int> b = std::move(a);
> std::cout << "a is engaged? " << !!a << std::endl;
> std::cout << "b is engaged? " << !!b << std::endl;
> return 0;
> }
>
> $ clang++ testOptional.cpp -o testOptional -std=c++17
> $ ./testOptional
> a is engaged? 1
> b is engaged? 1
>
> I would have expected:
> a is engaged? 0
> b is engaged? 1
>
> This impacts the standard std::optional implementation on my machine as well
> as the local copy in WebKit’s wtf/Optional.h.
>
> As far as I know, our convention in WebKit so far for our types has been that
> types getting moved-out are left in a valid “empty” state.
> As such, I find that std::optional’s move constructor behavior is error-prone.
>
> I’d like to know how do other feel about this behavior? If enough people
> agree this is error-prone, would we consider having our
> own optional type in WTF which resets the engaged flag (and never allow the
> std::optional)?
>
> Thanks,
> --
> Chris Dumez
>
>
>
>
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