[boost] Re: erroneous use of BOOST_STATIC_CONSTANT ?

From: David Abrahams (dave_at_[hidden])
Date: 2004-07-10 08:42:58

"John Maddock" <john_at_[hidden]> writes:

>> When using BOOST_STATIC_CONSTANT, the member still need to be _defined_
>> in a .cpp file (IIUC 9.4.2 par 4 of the standard), unless the enum-trick
>> is used, right?
>>
>> However gcc, intel-linux and the mipspro compiler (and probably others)
>> do not require a seperate definition. OTOH IBM/VisualAge does really
>> _need_ the definition (otherwise the symbols are undefined when linking).
>>
>> Would'nt it be better to advise library-developers to use an enum
>> instead of BOOST_STATIC_CONSTANT if their library does not contain a
>> definition?
>
> We've been through this before I think:
>
> We have one compiler (IBM's) that requires an out of line definition even
> when it's not required (and yes I realise it's a DR not the standard...
> yet), and another (Borland) which often gives the wrong result when an enum
> is used for compile time computations, and so *requires* the use of inline
> static constants and not enum's.  To complicate things further, compilers
> are required to allow any integral constant expression to be stored in an
> enum, but several (including IBM's) won't store anything wider than an int:
> this also makes enum's unsuitable for use as integral constants in many
> cases.
>
> So... I guess we're just going to have to use real integral constants with
> IBM and supply out of line definitions as needed?

I wonder if it's possible to use preprocessor tricks to have
BOOST_STATIC_CONSTANT generate enums (on IBM only) whenever they will
fit?  After all, integral constants _can_ be managed by the
preprocessor.

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com