static function pointers in C++ template class

static function pointers in C++ template class

[Wesley Smith]

Hi,
I'm trying to figure out the proper syntax for setting static member
variables of a C++ template class that are function pointers.  The
warnings from gcc don't really give any insight and a search of the
web turns up things that are close but not quite what I'm looking for.
 Here's the code:

template <class T>
class udata
{
	public:	

                  //stuff
	
	protected:
		static void (*kill_func)(T);   //my function pointer
};

//create specializations as well a general case
template <class T>
void (udata<T>::*kill_func)(T) = free;

template <dWorldID>
void (udata<dWorldID>::*kill_func)(dWorldID) = dWorldDestroy;

template <dSpaceID>
void (udata<dSpaceID>::*kill_func)(dSpaceID) = dSpaceDestroy;

The errors I'm getting are:

/Users/wesleysmith/jit.gl.lua_beta1/Lua_dev/ODE_Package/lua_ode_udata.h:62:
error: template declaration of 'void (udata<T>::* kill_func)(T)'
/Users/wesleysmith/jit.gl.lua_beta1/Lua_dev/ODE_Package/lua_ode_udata.h:65:
error: template declaration of 'void (udata<dxWorld*>::*
kill_func)(dxWorld*)'
/Users/wesleysmith/jit.gl.lua_beta1/Lua_dev/ODE_Package/lua_ode_udata.h:68:
error: template declaration of 'void (udata<dxSpace*>::*
kill_func)(dxSpace*)'

where dxSpace* is the same as dSpaceID and dxWorld* is the same as dWorldID

Where is my syntax going wrong?

thanks,
wes

Re: static function pointers in C++ template class

[Wesley Smith]

So, I kind of figured it out.  Now I'm seeing some strange behavior
with instantiation of  templated classes that is dependent on the
position of the code in the file.  If I have:

template <dSpaceID>
typename udata<dSpaceID>::fptr udata<dSpaceID>::kill_func = dSpaceDestroy;

template <dWorldID>
typename udata<dWorldID>::fptr udata<dWorldID>::kill_func = dWorldDestroy;

I get the error:
lua_ode.cpp:28: error: invalid conversion from 'void (*)(dxWorld*)' to
'void (*)(dxSpace*)'

If I swap the order of the 2 declarations, I get:

lua_ode.cpp:28: error: invalid conversion from 'void (*)(dxSpace*)' to
'void (*)(dxWorld*)'


Why would that happen?  My gcc version is:
gcc version 4.0.1 (Apple Computer, Inc. build 5341)

thanks,
wes