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On Mon, 22 Oct 2001, Luiz Henrique de Figueiredo wrote:

> If you use "getglobal" or "setglobal" tag methods, please send me a summary
> of how they are used. Thanks. --lhf

I use setglobal/getglobal for a user-defined floating-point type, so that
when Lua code assigns a number to a global that contains such a type, the
new value is stored in the existing userdata (instead of a lua number
replacing the userdata).


// C++ code

cfloat f("f", 1.0f);

	// Use f just like an ordinary float, with native speed and no
	// type checking or conversion.
	f += 10.0f;
	printf("%f\n", f);

-- Lua code:

	-- but the global 'f' is accessible to Lua as well...
	f = 27;		-- setglobal() invoked here.
	print(f);	-- getglobal() invoked here.

// Here's the cfloat setglobal tag method:

static int	cfloat_set( lua_State* L )
// Lua CFunction which sets the value of the given cfloat to the given lua
// number.
	// arg 1: varname
	// arg 2: previous var value (in this case the cfloat*)
	// arg 3: new var value

	cfloat*	cf = static_cast<cfloat*>( lua_touserdata( L, 2 ) );
	*cf = lua_tonumber( L, 3 );

	return 0;

The getglobal tag method is similarly trivial.

I'd be much happier if setglobal/getglobal were replaced by generic
"setvalue/getvalue" tag methods, which would be called whenever Lua tried
to get/set a tagged type.  That way I could embed cfloats in tables
without the table having to know about it.

I'm still feeling my way towards a good transparent C++/Lua binding, so
this may not be the best way to do what I'm trying to do.