Re: class static constants, mpl, and linker problems
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
On Tuesday, January 27, 2004, at 01:45 PM, Daniel Krügler wrote:
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??
As far as I know, Boost currently provides these definitions for all static member constants that you ask for. If you find one that is missing it should be reported to the author as a bug. If, on the other hand, you use the BOOST_STATIC_CONSTANT macro in your own classes you are of course required to add the definition yourself.
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.
For that you'll have to ask people who know more about Windows compilers. Since I do not use Windows but just MacOS, Unix and Linux I cannot help with bugs or compiler options of that compiler. Matthias
As far as I know, Boost currently provides these definitions for all static member constants that you ask for. If you find one that is missing it should be reported to the author as a bug. If, on the other hand, you use the BOOST_STATIC_CONSTANT macro in your own classes you are of course required to add the definition yourself.
Actually that was my basic assertion and I asked for it correctness. Your first answer implied, that I have to provide that definition on my own (at least for me), this one says otherwise. If you are right, than boost is prepared for every compliant C++ compiler, but (I **assume** again) regrettably not for the currently state-of-the-art Microsoft compiler VC7.1.
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.
For that you'll have to ask people who know more about Windows compilers. Since I do not use Windows but just MacOS, Unix and Linux I cannot help with bugs or compiler options of that compiler.
It wasn't meant as an offense, please accept my apologies for my rough tone. Thanks, Daniel
participants (3)
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Daniel Krügler -
Matthias Troyer