Re: Trouble binding a class - should be simple

On 05/05/2011 09:48, feng qiu wrote:
> Please try v*:*getX().
>
> On 5 May 2011 15:56, Simon Pickles <[email protected] 
> <mailto:[email protected]>> wrote:
>
>
>     Hello,
>
>     I am trying to expose part of the btVector3 class from
>     BulletPhysics to Lua:
>
>     http://www.bulletphysics.com/Bullet/BulletFull/classbtVector3.html
>
>     My first attempt:
>
>     // C++
>       void RegisterPhysicsTypesWithLua( lua_State* lua )
>       {
>         module( lua )
>         [
>           class_<btVector3>( "btVector3" )
>           .def( "getX",&btVector3::getX )
>           .def( "getY",&btVector3::getY )
>           .def( "getZ",&btVector3::getZ )
>           .def( "setX",&btVector3::setX )
>           .def( "setY",&btVector3::setY )
>           .def( "setZ",&btVector3::setZ )
>         ];
>       }
>
>     --Lua
>     print("Testing btVector3 in lua")
>     v = btVector3()
>     print("btVector3 created")
>
>     print( "x = " .. v.getX() )  -- should print x = 0.0
>     v.setX(99.9)
>     print( "x = " .. v.getX() )  -- should print x = 99.9
>
>     ------------------------------------------
>     This first attempt produces the error:
>     "Attempt to call a nil value"
>
>
>     So I added a constructor and tried again:
>
>     // C++
>       void RegisterPhysicsTypesWithLua( lua_State* lua )
>       {
>         module( lua )
>         [
>           class_<btVector3>( "btVector3" )
>           .def( constructor<  float, float, float>() )
>           .def( "getX",&btVector3::getX )
>           .def( "getY",&btVector3::getY )
>           .def( "getZ",&btVector3::getZ )
>           .def( "setX",&btVector3::setX )
>           .def( "setY",&btVector3::setY )
>           .def( "setZ",&btVector3::setZ )
>         ];
>       }
>
>     --Lua
>     print("Testing btVector3 in lua")
>     v = btVector3(1.0,2.0,3.0)
>     print("btVector3 created")
>
>     print( "x = " .. v.getX() )  -- should print x = 1.0
>     v.setX(99.9)
>     print( "x = " .. v.getX() )  -- should print x = 99.9
>
>     ------------------------------------------
>     This second attempt produces the error:
>     "No such operator defined"
>
>
>     I have double checked that I am definately calling the
>     RegisterPhysicsTypesWithLua with the correct LuaState.
>
>     I expected this to be reasonably trivial as I have been exposing
>     my own
>     classes with ease. This is however, the first time I have tried to
>     expose a 3rd party class. Am I missing something obvious?
>
>     Thanks very much
>
>     Simon
>
Well spotted (too used to Python!). The second version works!

However doesn't explain why the first version (with default ctor) fails. 
It never gets to the getX() call:
Testing btVector3 in lua
Error: Attempt to call a nil value


btVector3 does indeed have a default ctor:
http://www.bulletphysics.com/Bullet/BulletFull/classbtVector3.html#a82b4c5da54ecd4c91bd9b056dea0d288

Thanks

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