variant warnings?
Does Boost.Variant require certain warnings to be disabled? The following program generates a warning for me with VC9: COMPILER INPUT: #include <boost/variant.hpp> #include <iostream> struct vis : public boost::static_visitor<> { void operator()( int & ) const { std::cout << "int" << std::endl; } void operator()( std::string & ) const { std::cout << "string" << std::endl; } }; int main( int, char * ) { boost::variant< int, std::string > v; boost::apply_visitor( vis(), v ); return 0; } COMPILER OUTPUT: 1>Compiling... 1>variant_basic.cpp 1>J:\work\ext\boost_ext\boost/variant/variant.hpp(894) : warning C4512: 'boost::detail::variant::invoke_visitor<Visitor>' : assignment operator could not be generated 1> with 1> [ 1> Visitor=const vis 1> ] 1> J:\work\ext\boost_ext\boost/variant/variant.hpp(1771) : see reference to class template instantiation 'boost::detail::variant::invoke_visitor<Visitor>' being compiled 1> with 1> [ 1> Visitor=const vis 1> ] 1> J:\work\ext\boost_ext\boost/variant/detail/apply_visitor_unary.hpp(72) : see reference to function template instantiation 'void boost::variant<T0_,T1>::apply_visitor<const Visitor>(Visitor &)' being compiled 1> with 1> [ 1> T0_=int, 1> T1=std::string, 1> Visitor=vis 1> ] 1> ..\indep\variant_basic.cpp(11) : see reference to function template instantiation 'void boost::apply_visitor<vis,boost::variant<T0_,T1>>(const Visitor &,Visitable &)' being compiled 1> with 1> [ 1> T0_=int, 1> T1=std::string, 1> Visitor=vis, 1> Visitable=boost::variant<int,std::string> 1> ]
AMDG hfye-wila@spamex.com wrote:
Does Boost.Variant require certain warnings to be disabled? The following program generates a warning for me with VC9:
Warning 4512 is almost always harmless. It's usually caused by structs containing reference members. You're best off disabling it. In Christ, Steven Watanabe
As recommended (thanks Steve!), I have disabled VC9's C4512 warning to get a canonical Boost.Variant example to compile (in VC9) without warnings: #pragma warning( push ) #pragma warning( disable : 4512 ) #include <boost/variant.hpp> #pragma warning( pop ) #include <iostream> using namespace std; struct vis : public boost::static_visitor<> { void operator()( int & ) const { cout << "int" << endl; } void operator()( string & ) const { cout << "string" << endl; } }; int main( int, char * ) { boost::variant< int, string > v; boost::apply_visitor( vis(), v ); return 0; } *If* this warning is truly harmless, should this be considered a bug in Boost.Variant? Shouldn't Boost.Variant disable benign warnings in a compiler-independent way? Or at least shouldn't the Boost.Variant docs be updated? Or is this warning part of Boost.Variant's design? If so is there any way I can change my code above to compile without warnings other without explicitly suppressing warnings? Any Boost.Variant authors/maintainers care to comment? John Fearnside -----Original Message----- AMDG hfye-wila@spamex.com wrote:
Does Boost.Variant require certain warnings to be disabled? The following program generates a warning for me with VC9:
Warning 4512 is almost always harmless. It's usually caused by structs containing reference members. You're best off disabling it. In Christ, Steven Watanabe
AMDG hfye-wila@spamex.com wrote:
*If* this warning is truly harmless, should this be considered a bug in Boost.Variant?
I consider this a low priority bug.
Shouldn't Boost.Variant disable benign warnings in a compiler-independent way?
This warning is Visual Studio specific. In Christ, Steven Watanabe
I agree with Steve that the C4512 warning is a low-priority bug: it is easily worked around and it's only a level 4 warning. But, I must not be understanding Boost.Variant (1.35.1) because the following simple example generates several other VC9 warnings: C4345 (level 2) and C4100 (level 4): #include <boost/config.hpp> #ifdef BOOST_MSVC # pragma warning( push ) # pragma warning( disable : 4512 ) #endif #include <boost/variant.hpp> #ifdef BOOST_MSVC # pragma warning( pop ) #endif #include <iostream> using namespace std; struct C1 {}; struct C2 {}; struct vis : public boost::static_visitor<> { void operator()( C1 & ) const { cout << "C1" << endl; } void operator()( C2 & ) const { cout << "C2" << endl; } }; int main( int, char * ) { boost::variant< C1, C2 > v; boost::apply_visitor( vis(), v ); return 0; } Disabling these in the manner above works but I'm hoping one of its authors/maintainers can comment on intended usage of Boost.Variant with VC9? I'm wary of disabling each warning I encounter. That makes it difficult for me to know which warnings are known to be harmless and which indicate errors in my code. BTW: By "compiler-independent way" I mean using <boost/config.hpp> macros to wrap compiler-specific pragmas (as above). John Fearnside -----Original Message----- AMDG hfye-wila@spamex.com wrote:
*If* this warning is truly harmless, should this be considered a bug in Boost.Variant?
I consider this a low priority bug.
Shouldn't Boost.Variant disable benign warnings in a compiler-independent way?
This warning is Visual Studio specific. In Christ, Steven Watanabe _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
AMDG hfye-wila@spamex.com wrote:
I agree with Steve that the C4512 warning is a low-priority bug: it is easily worked around and it's only a level 4 warning. But, I must not be understanding Boost.Variant (1.35.1) because the following simple example generates several other VC9 warnings: C4345 (level 2) and C4100 (level 4):
<snip>
Disabling these in the manner above works but I'm hoping one of its authors/maintainers can comment on intended usage of Boost.Variant with VC9? I'm wary of disabling each warning I encounter. That makes it difficult for me to know which warnings are known to be harmless and which indicate errors in my code.
C4345 is a backwards compatibility warning. The compiler is issuing a warning because it treats new int() correctly using value-initialization! You can ignore this unless you care about compatibility with VC6. C4100 (unused variable) is a legitimate warning, but it fires for this: tempate<class T> void destory(T& t) { t.~T(); } even though t is used. It should be safe to disable it for Boost headers. In Christ, Steven Watanabe
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