Re: [boost] [iterator] could non-small predicates/functors be stored as boost::optional<T> to avoid double construction?

Subject: Re: [boost] [iterator] could non-small predicates/functors be stored as boost::optional<T> to avoid double construction?
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2008-09-04 15:32:29

AMDG

David Abrahams wrote:
>> There is still some value in storing functors in optional<T>:
>> boost.lambda expressions are not asignable, thus rendering any
>> iterator that contains a lambda does no longer meet the requirements
>> of  Assignable of which TrivialIterator is a refinement of.
>>
>> It is easy to add a wrapper around optional<T> that makes it
>> Assignable as long as T is copy constructible (which lambdas are), so
>> it can be used as a quick workaround for this problem.
>>     
>
> But for that you wouldn't need the bool in optional.
>   

I think that you do need it, actually.
I assume that assignment would be implemented with destroy + reconstruct?
In this case, you need to deal with the possibility of the copy 
constructor throwing.

In Christ,
Steven Watanabe