Re: [boost] [iterator] reverse_iterator<counting_iterator<T>>

Subject: Re: [boost] [iterator] reverse_iterator<counting_iterator<T>>
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2010-04-13 09:55:15

Arno Schödl wrote:
> "Stewart, Robert" <Robert.Stewart_at_[hidden]
>
> > this->base() calls iterator_adaptor<>::base(), which
> > returns a reference to the underlying iterator it holds.
> > Passing that reference to boost::prior() means that prior()
> > pre-decrements the iterator within the iterator_adaptor.  It
> > would be odd for that
>
> >decrement operator to return anything but a reference to the
> > decremented object, so boost::prior() returns a reference to
> > its decremented argument, a reference to the decremented
> > iterator within the iterator_adaptor.
>
> > I see no problem.
>
> boost::prior(...) internally makes a copy of its iterator
> argument, decrements it and returns it by value, so far so
> good. counting_iterator::operator* then returns a reference
> into this (temporary) iterator. Returning from
> reverse_iterator::dereference() destroys the temporary
> iterator, but still returns the reference pointing into it.

boost::prior's T is deduced as a reference type.  The copy is of a reference.  There's no temporary.

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer, Core Software      using std::disclaimer;
Susquehanna International Group, LLP  http://www.sig.com

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