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Subject: Re: [boost] Boost and exceptions
From: Dave Abrahams (dave_at_[hidden])
Date: 2012-06-23 15:46:22

on Sat Jun 23 2012, Nathan Ridge <> wrote:

> By the way, my first thought when I encountered this problem
> is that C++11 ought to have specified the range-based for loop
> in such a way that the lifetime of temporaries in the range
> expression is extended for the duration of the loop.
> Does anyone share this opinion?

+0. I don't know enough to have an opinion yet.

> Would there be any downsides to this?

Well of course there would. Extending the lifetime of a non-trivial temporary
beyond what's needed creates inefficiencies (memory pressure, register
pressure, worse locality of reference...)

> It is also interesting to note that boost::for_each together
> with a lambda - a from to which any range-based for loop can
> easily be converted - does not suffer from this problem. I think
> this corroborates the fact that the range-base for loop is
> suboptimally specified in the standard - after all the range-
> based for loop was meant to replace things like boost::for_each.

You have a point... though maybe what we really need is
expression-statements ;-)

Dave Abrahams
BoostPro Computing

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