Re: [devel] boost: SimGear

["Ivan A. Melnikov" <iv@altlinux.org>]

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On Thu, 6 Sep 2012 10:47:23 +0300
Michael Shigorin <mike@osdn.org.ua> wrote:

> On Wed, Sep 05, 2012 at 10:01:18PM +0000, ALT beekeeper wrote:
> > SimGear-2.8.0-alt1
> > 	/usr/src/RPM/BUILD/SimGear-2.8.0/simgear/scene/material/Effect.cxx:708:67:
> > instantiated from here
> > 	/usr/include/boost/functional/hash/extensions.hpp:257:34:
> > error: no matching function for call to 'hash_value(const
> > osg::Shader::Type&)' /usr/include/boost/functional/hash/extensions.hpp:257:34:
> > note: candidates are:
> 
> А с этим что делать?
> 

В принципе, сборка чинится приложенным патчем, но мне он не нравится.
История на английском, на случай связи с апстримом:

Since boost 1.51.0 boost::hash_value is implemented using SFINAE to
avoid implicit casts to built in types when calling it [1]. Because of
that compiler can't use boost::hash_value(int) for enum
osg::Shader::Type any more. Thus one can't use osg::Shader::Type as a
(part of) key for boost::unordered_map.

The proper solution is to overload hash_value function for
osg::Shader::Type as described in [2]. This function should be found via
argument dependent lookup (ADL), so it must be defined in osg namespace.
I don't know if it is appropriate for OpenSceneGraph to add it (also it
should not hurt), and how it should be implemented in that case. So in
my patch I put it right into simgear/scene/material/Effect.cxx, which of
course is a dirty hack.

Maybe, the best solution would be to change implementation of
hash_value(const ProgramKey& key) (simgear/scene/material/Effect.cxx,
line 712).

References:

[1] http://www.boost.org/users/history/version_1_51_0.html
[2] http://www.boost.org/doc/libs/1_51_0/doc/html/hash/custom.html

-- 
WBR,
Ivan A. Melnikov

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diff --git a/SimGear/simgear/scene/material/Effect.cxx b/SimGear/simgear/scene/material/Effect.cxx
index 2e10318..5c839d6 100644
--- a/SimGear/simgear/scene/material/Effect.cxx
+++ b/SimGear/simgear/scene/material/Effect.cxx
@@ -76,6 +76,14 @@
 #include <simgear/structure/SGExpression.hxx>
 #include <simgear/props/vectorPropTemplates.hxx>
 
+namespace osg
+{
+    std::size_t hash_value(osg::Shader::Type t)
+    {
+        return boost::hash_value(static_cast<int>(t));
+    }
+}
+
 
 namespace simgear
 {