Re: [boost] [iterator] function_output_iterator constructed from a lambda function is not assignable

Subject: Re: [boost] [iterator] function_output_iterator constructed from a lambda function is not assignable
From: Paul Fultz II (pfultz2_at_[hidden])
Date: 2016-02-15 15:01:17

On Sunday, February 14, 2016 at 9:18:15 PM UTC-6, Peter Dimov wrote:
>
> Paul Fultz II wrote: 
>
> > One way to deal with this is to put it into boost::optional. 
>
> boost::optional<T> uses T::operator= when the source and the target hold a 
> value. 
>

It seems that boost::optional is not constrained properly, the following
compiles just fine:

struct not_assignable
{
    not_assignable& operator=(const not_assignable&)=delete;
};
static_assert(!std::is_copy_assignable<not_assignable>(), "Assignable");
static_assert(std::is_copy_assignable<boost::optional<not_assignable>>(), 
"Not Assignable");

However, if I use the assignment operator, it breaks with a compile error.
Either way `boost::optional` should fallback on in-place new, when there is 
no
assignment operator.

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