Re: LuaBind Function Default Values

The other option is to overload the function in Lua, and use Lua's
optional argument handling.  For example:


// the defaults here are not strictly required for this method to work.
int somefunc( bool p1=true, bool p2=false );

luabind::module(L) [ def( "somefunc", &somefunc ) ];

---------------8<-----------------
-- Lua

oldsomefunc = somefunc
function somefunc( p1, p2 )
	if type(p1) == 'nil' then p1 = true end
	if type(p2) == 'nil' then p2 = false end
	oldsomefunc( p1, p2 )
end

-- Use it.
somefunc()
somefunc( false )
somefunc( true, true )

-------------------8<------------------

Note that for other types besides boolean, you could get away with:

local p1 = p1 or 'default_value'

This does not work with booleans as 'false' gets replaced with the
default.

HTH

Nigel Atkinson


On Tue, 2010-08-31 at 13:51 -0300, Julio Cesar Cunha wrote:
> I see this solution yesterday, i think i don't have much choise.
> 
> Others solution that i find is set many casts like this:
> 
> .def("beginScene", (bool
> (IVideoDriver::*)())&IVideoDriver::beginScene)
> .def("beginScene", (bool
> (IVideoDriver::*)(bool,bool))&IVideoDriver::beginScene) 
> .def("beginScene", (bool
> (IVideoDriver::*)(bool,bool,bool,bool))&IVideoDriver::beginScene) 
> 
> This solution work well with this type of parameter, but if you need
> to send a point the program crash, because lua send trash to the
> point.
> 
> Thanks Daniel, i'm waiting the 1.0 version.
> 
> 2010/8/31 Daniel Wallin <[email protected]>
>         On Mon, Aug 30, 2010 at 11:07 PM, Julio Cesar Cunha
>         <[email protected]> wrote:
>         
>         > I think that is the solution, but in this way i will redo
>         all.
>         >
>         > Strange that luabind don't suporte this feature yet,
>         searching on google i
>         > found some binds that do that, like toLua++ and
>         Boost:Python.
>         >
>         > Anyway, Don't rasterbar don't say nothing about this
>         feature? maybe in some
>         > future update.
>         
>         
>         The problem is that it isn't technically possible to detect
>         and use
>         the default values. They are not part of the function
>         signature.
>         Boost.Python supports default values by generating a set of
>         overloads
>         with different arities using a macro (from docs):
>         
>          BOOST_PYTHON_FUNCTION_OVERLOADS(foo_overloads, foo, 1, 4)
>         
>         I'm planning to support default values in 1.0 by letting the
>         user pass
>         the values to def(), possibly using this syntax:
>         
>          def("f", &f, _2 = "default value")
>         
>         But for now, the only solution is to define thin wrapper
>         functions.
>         This is pretty easy to do, but not ideal of course:
>         
>          class X
>          {
>          public:
>              void f(int x = 0, int y = 0);
>          };
>         
>          void f0(X& self)
>          {
>              self.f();
>          }
>         
>          void f1(X& self, int x)
>          {
>              self.f(x);
>          }
>         
>          void f2(X& self, int x, int y)
>          {
>              self.f(x, y);
>          }
>         
>          ...
>         
>          class_<X>("X")
>              .def("f", &f0)
>              .def("f", &f1)
>              .def("f", &f2)
>         
>         --
>         Daniel Wallin
>         BoostPro Computing
>         http://www.boostpro.com
>         
>         
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> 
> 
> -- 
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> 
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