Userdata and GC

[Ty Matthews <tmatthews3@...>]

I have a few Userdata implementation questions related to the C API, with 5.0.  Included at the bottom is some code.

1.  Is it safe to assume that Lua will free the memory that is allocated by lua_newuserdata(), if I do nothing more than this?
2.  Are there any caveats that I should be aware of when letting Lua free the allocated block, especially in the realm of C++?  IE, if I put a class in my struct, will the destructor be called, etc?  
3.  If lua_newuserdata() returns NULL, what can I assume about the stack?  Does anything get pushed onto the stack in the case of a failure?
4.  Are there any sample programs out there that detail how to set a GC metamethod so I can try and free my own memory?  Is there a general rule for when you should and should not free your own memory?

Sorry for the question spam.  I've been using Lua in a program of mine for close to a year now.  I just recently moved to 5.0 and started to get into some more advanced topics.  This Userdata concept is new to me, and I haven't gotten a grip on it just by reading the manual.

Thanks for any help-

   Ty



class CMyClass
{
  ....  // assume some implementation
};

int MyTest( lua_State *pState )
{
    typedef struct
    {
        int i;
        CMyClass MyClass;
    } MyStruct, *LPMyStruct;
    
    int iPush = 0;
    int iTop = lua_gettop( pState );
    LPMyStruct lpMyStruct = NULL;
    void *pUserData = lua_newuserdata( pState, sizeof( MyStruct ) );
	
    if( pUserData )
    {
        iPush++;
        lpMyStruct = static_cast< LPMyStruct >( pUserData );
        ....  // do stuff with the struct members; initialize, etc.
    }	
    return iPush;
}