Re: [boost] [variant] Please vote for behavior (Was: Basic rvalue and C++11 features seupport)

Subject: Re: [boost] [variant] Please vote for behavior (Was: Basic rvalue and C++11 features seupport)
From: Krzysztof Czainski (1czajnik_at_[hidden])
Date: 2013-01-21 10:19:08

2013/1/21 Antony Polukhin <antoshkka_at_[hidden]>

> Current implementation of recursive_wrapper move constructor is not
> optimal:
>
> recursive_wrapper<T>::recursive_wrapper(recursive_wrapper&& operand)
>     : p_(new T(std::move(operand.get()) ))
> { }
>
> During descussion were made following proposals:
>
[...]

II: Set operand.p_ to NULL, add BOOST_ASSERT in get operations
>

I vote for II, because:

  + good performance
>   + provides noexcept guarantee for move constructor
>   + optimization will be used even if varinat has no type with trivial
> default constructor
>   + easy to implement
>

And the above 4 points mean to me that it is a simple solution, which does
the job.

  - triggers an assert when user tries to reuse moved object
>

Yes, using the moved object in other cases then assigning something to it
is UB, so that's the right thing to do ;-)

  - adds an empty state to the recursive_wrapper

This empty state can only be achieved by moving from the object, right?
That's fine with me.

Regards,
Kris