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

From: Daniel Krügler (dsp_at_[hidden])
Date: 2004-01-27 07:45:27

Hello Matthias,

Matthias Troyer schrieb:
> 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,

No, it doesn't, please read the original thread carefully. I am aware of 
the fact, that an integral or enumeration type static member needs a 
corresponding definition and I hope my contribution has made that clear 
to everyone.
Your answer implies, that users of the boost library are responsible for 
providing these definitions for boost constants. If so, I think that 
would be bad news. Consider those many hidden constants in whatever 
boost::details namespace or other implementation-dependent data items. 
How should the boost user correctly provide the necessary definitions? 
To my opinion boost should at least provide in the libs section source
files with possibly necessary definitions of all externally accessible
constants, which the user can translate if necessary.
I also want to add, that although my example seems artifical, it should
show a basic problem. Consider a simple "algorithm" like std::max which
takes constant references as arguments. You cannot demand, that boost
users must watch out for those or similar expressions in their code and
take proper resolutions by hand??

Second, your response did not take into account the problems with the
effects of the /Ze and /Za flags of the current VC7.1 compiler which I 
also think is a very important issue.

Daniel