[boost] Re: class static constants, mpl, and linker problems

From: Daniel Krügler (dsp_at_[hidden])
Date: 2004-01-27 08:39:44

Hello David,

David Abrahams schrieb:
> Matthias Troyer <troyer_at_[hidden]> writes:
> 
> 
>>Dear Daniel,
>>
>>If you use BOOST_STATIC_CONSTANT you need to additionally provide a
>>definition on conforming compilers. The correct usage is like in:
>>
>>// declaration
>>class A {
>>   BOOST_STATIC_CONSTANT(int , x=1);
>>};
>>
>>....
>>
>>//definition
>>#ifndef BOOST_NO_INCLASS_MEMBER_INITIALIZATION
>>int A::x;
>>#endif
>>
>>
>>I hope that clarifies this issue,
> 
> 
> Another approach is to use mpl::int_<n> or integral_c<T,n> which
> supply the definitions themselves.
> 

So you mean, if I use integral_c<T,n>::value, the definition of value
is provided by boost?
According to my assumptions (which might be wrong, as I said) here 
applies the same problem, because integral_c<T,n> also contains a 
BOOST_STATIC_CONSTANT and thus a possibly addressable object, but I am
willing to be corrected, of course.

To make my request more clear: I am **not** speaking of a programming
style which **should** take advantage of using integral_c<T,n> instead
of an addressable (constant) object, I am speaking of daily programming
practice. Since e.g. integral_c<T,n>::value is not a boost-internal
"you-should-not-use-or-you-are-fired", it seems legal code to write
something like

const long myvalue = foo(); // run-time determined value
const long max_value = std::max(myvalue,
   boost::mpl::integral_c<long,15>::value); // Combine compile-time and
                                            // run-time information here

without knowing too much about the internals of boost::mpl (besides the
fact, that it might be necessary to additionally add some further mpl
source files into my project).

Greetings,

Daniel