Re: [Boost-users] [Range & c++0x Lambdas] Can this be done?

On 11/21/2012 11:27 AM, Nathan Ridge wrote:

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On Wed, Nov 21, 2012 at 5:15 PM, Nathan Crookston mailto:nathan.crookston@gmail.com> wrote: Rob,

On Wed, Nov 21, 2012 at 6:39 AM, Robert Jones mailto:robertgbjones@gmail.com> wrote: Can the last line, labelled NOT Ok, be made to work? I think the lambda does not publish its result as a bind does, so I suspect it's hopeless. Any thoughts? // NOT Ok boost::range::push_back( out, in | transformed( []( S & s ) { return s.i; } ) ); }

It seems trivial to have a nested result_type in all cases with a lambda. However, in C++11 there's no need for it due to decltype.

Sadly, some compilers fall into a gap where result_of (boost or std) doesn't use decltype and lambdas don't publish tr1-style result_type -- leaving code like the above in the lurch.

Michel Morin wrote some code for adapting such a case which may be of interest to you: http://lists.boost.org/boost-users/2012/01/72879.php

Right, thank you for that informative explanation. So, several solutions, non perfect. Choose your poison!

- Rob.

I've been turning on BOOST_RESULT_OF_USE_DECLTYPE for such occasions and haven't had any problems with it.

It's *mostly* safe on *most* modern compilers to do that. Boost has been very cautious about rolling out its decltype-based result_of implementation because "mostly" doesn't cut it. But starting with 1.52, it's enabled by default on clang 3.1 and higher. More compilers will be added as their decltype support improves. -- Eric Niebler BoostPro Computing http://www.boostpro.com