Re: [boost] [Config] Macro for C++0x range-based for

Subject: Re: [boost] [Config] Macro for C++0x range-based for
From: Sebastian Redl (sebastian.redl_at_[hidden])
Date: 2010-12-17 15:27:29

On 17.12.2010, at 17:35, Michel MORIN wrote:

> Sebastian Redl wrote:
>>> C++0x range-based for is available on GCC 4.6 (Pre-release).
>>> There is no BOOST_NO_RANGE_BASED_FOR macro,
>>> so I made a patch against trunk and made a test case. Please see
>>> attached files.
>>> Is it reasonable to add this macro?
>> 
>> I don't think there's really a point, unless you want Boost's users to use
>> the config macros. Range-based for is a convenience functionality, not an
>> enabling functionality. In other words, if you can't use it all the time,
>> but have to write the long form anyway, what's the point in using it?
> 
> Range-based for conflicts with many Boost libraries.
> This issue can be resolved by fixing boost/range/begin.hpp and
> boost/range/end.hpp,
> which needs BOOST_NO_RANGE_BASED_FOR macro.

No, a standard library that provides std::begin() and std::end() conflicts with boost::begin() and boost::end() provided by Boost.Range. These functions are used by for-range, so their existence is a requirement for a compiler supporting for-range on anything but arrays, but the language feature itself has nothing to do with the conflict. This is important because, for example, libc++ already has std::begin() and std::end(), but Clang doesn't yet support for-range.

> 
> Yeah, we can always use BOOST_FOREACH instead of range-based for.
> And considering portability, BOOST_FOREACH is a must.
> But IMHO it's a pity that users of the Boost libraries are recommended
> not to use a language feature.

Er, what? Who recommended that Boost users not use a language feature? Dave merely said that Boost authors should just use BOOST_FOREACH.

Sebastian