Re: [boost] [config] C++0X Compiler doesn't support classes with constructors in unions

Subject: Re: [boost] [config] C++0X Compiler doesn't support classes with constructors in unions
From: Vicente Botet (vicente.botet_at_[hidden])
Date: 2011-02-23 10:48:37

Beman Dawes wrote:
> 
> On Tue, Feb 22, 2011 at 5:06 PM, Vicente Botet
> <vicente.botet_at_[hidden]>wrote:
> 
>>
>> Hi,
>>
>> is there a macro that can be tested to know if a compiler doesn't support
>> classes with constructors in unions?
>>
>>
> No, and GCC 4.6 is supporting them. See
> http://gcc.gnu.org/projects/cxx0x.html
> 
> The macro might be named BOOST_NO_UNRESTRICTED_UNIONS.
> 
> See http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2544.pdf
> 
> Do you have an actual need for such a macro? We only want to add macros
> that
> will be actually used by Boost libraries.
> 

I was testing your Endian library and the macro used to know if constructors
shouldn't be used for the endian class is up to now

# if defined(BOOST_NO_DEFAULTED_FUNCTIONS) &&
defined(BOOST_ENDIAN_FORCE_PODNESS)
#   define BOOST_ENDIAN_NO_CTORS
# endif

I tested with gcc 4.4/4.5.1 c++0x with BOOST_ENDIAN_FORCE_PODNESS defined
and the union test fails.

This should mean that for these versions  BOOST_NO_DEFAULTED_FUNCTIONS is
not defined so the constructors are defined.

Shouldn't you use BOOST_NO_UNRESTRICTED_UNIONS  instead of
BOOST_NO_DEFAULTED_FUNCTIONS in this case?

> If you do have a need, would you like to try your hand at providing the
> macro, test cases, docs, etc?
> 

Yes, I know the process :). Unfortunately I don't have access to gcc 4.6 now
(my hard drive was broken :( ), so I can not test it now. I will see once I
reach to reinstall a 4.6 version on my new computer.

Best,
Vicente
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