Re: [Gnash-dev] Truly bizarre warning in compiling LineStyle.cpp

[strk]

Which boost version and compiler version ?
No warnings with
  g++ (Ubuntu 4.3.2-1ubuntu12) 4.3.2
  boost 1.34.1-11ubuntu1

--strk;

On Sun, Aug 08, 2010 at 04:01:25PM -0700, John Gilmore wrote:
> In libcore/LineStyle compile:
> 
>   CXX    LineStyle.lo
> FillStyle.h: In member function ‘void 
> gnash::LineStyle::read(gnash::SWFStream&, gnash::SWF::TagType, 
> gnash::movie_definition&, const gnash::RunResources&)’:
> FillStyle.h:274: warning: dereferencing pointer ‘<anonymous>’ does break 
> strict-aliasing rules
> /usr/include/boost/variant/detail/cast_storage.hpp:33: note: initialized from 
> here
> FillStyle.h: In member function ‘void 
> gnash::LineStyle::read_morph(gnash::SWFStream&, gnash::SWF::TagType, 
> gnash::movie_definition&, const gnash::RunResources&, gnash::LineStyle*)’:
> FillStyle.h:274: warning: dereferencing pointer ‘<anonymous>’ does break 
> strict-aliasing rules
> /usr/include/boost/variant/detail/cast_storage.hpp:33: note: initialized from 
> here
> FillStyle.h:274: warning: dereferencing pointer ‘<anonymous>’ does break 
> strict-aliasing rules
> /usr/include/boost/variant/detail/cast_storage.hpp:33: note: initialized from 
> here
> 
> So, bizarre things:
> 
>   *  The source file and line number in error is never mentioned.
>   *  The warning is on FillStyle.h:274 which is the innocuous Return line in:
> 
>     /// Get the color of the fill.
>     rgba color() const {
>         return _color;
>     }
> 
>   *  By random inspection, the problem seems to be this code:
> 
>         // TODO: store a fill style properly, removing the need for the
>         // visitor.
>         m_color = boost::apply_visitor(GetColor(), fp.first.fill);
>         pOther->m_color = boost::apply_visitor(GetColor(), fp.second->fill);
> 
> which invokes some odd code at the top of LineStyle.cpp:
> 
> class GetColor : public boost::static_visitor<rgba>
> {
> public:
>     rgba operator()(const SolidFill& f) const {
>         return f.color();
>     }
>     rgba operator()(const GradientFill&) const {
>         return rgba();
>     }
>     rgba operator()(const BitmapFill&) const {
>         return rgba();
>     }
> };
> 
>   *  It's not actually clear what the compiler's error means.
> 
> I can't tell what this is doing, and all the Boost documentation for
> it is complete gobbledygook ("Visitor Concept: Given
> variant<T1,T2,...,Tn>, a function object which unambiguously accepts
> any value of each of the variant's bounded types, is a Visitor of of
> the variant.")  It looks to me like a perfect example of how 
> object-oriented design can completely obscure the meaning of some
> probably-straightforward code.
> 
> Should someone who understands this clean it up so the compiler
> doesn't complain about it?
> 
>       John
> 
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