Re: [boost] [optional] problems with swap()

From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2008-04-10 17:32:23

Niels Dekker - mail address until 2008-12-31 skrev:
> Thorsten Ottosen wrote:
>> No user expects swap to throw or invalidate iterators or references like
>> the current implementation does.
> 
> I do agree that it's a pity that the current implementation of
> optional::swap might throw an exception.  Still, like Andrey Semashev,
> I'd rather not have it require T to be default constructible.  Because I
> can imagine that people typically use optional<T> for a
> non-DefaultConstructible T.  (A nice thing about boost::optional<T> is
> that it provides a default constructor, even for those types T that
> don't have one.)

Right, this is certainly true, but this is not the same as "none of the 
functions in optional's interface can/should require default constructible".

> What would you think of having boost::optional implemented by holding a
> pointer to T, instead of an aligned_storage object and a m_initialized
> flag?  It would manage the memory that the pointer would point to. 
> Having NULL would indicate being uninitialized. (I admit it's a rather
> theoretical question, because I don't even know if Fernando would like
> such an approach...)

Going for a heap based implementation is out of the question for 
performance reasons.

-Thorsten