Re: [luabind] Custom policies [2/2]

[Dan P. <dpo...@ar...>]

The only_accepts_values structure was added by me to generate a
compile-time error on incorrect use (the other Luabind policies do
similar things when they are designed to only take a pointer or
reference etc.).

 

Without it, the program would compile if you used a pointer/reference
with the policy but Luabind would assert and halt when you tried to use
it at run-time.

 

It's a shame the code base is so arcane... I'd love to go and make more
sophisticated improvements to it but 90% of the time I don't even know
where to begin. :(

 

Dan. 

 

From: lua...@li...
[mailto:lua...@li...] On Behalf Of Josh
Green
Sent: Monday, May 12, 2008 5:26 PM
To: lua...@li...
Subject: Re: [luabind] Custom policies [2/2]

 

Mate,
That looks fantastic, awesome work.
Sorry I don't have the change to play with the by value/reference
stuff.. But I imagine it would either be a template specialisation
thing, or you have this type in your conversion policy:
struct only_accepts_values {};

I assume that stops Luabind from using the class with references... What
happens if you use something else or nothing in it's place?

Like I said, awesome work!

Josh

________________________________

> Date: Thu, 8 May 2008 16:46:28 -0700
> From: dpo...@ar...
> To: lua...@li...
> Subject: Re: [luabind] Custom policies [2/2]
> 
> Here's the contents of the new file, cast_policy.hpp:
> 
> #ifndef LUABIND_REINTERPRET_CAST_POLICY_HPP_INCLUDED
> #define LUABIND_REINTERPRET_CAST_POLICY_HPP_INCLUDED
> 
> #include <luabind/config.hpp>
> #include <luabind/detail/policy.hpp>
> 
> namespace luabind { namespace detail {
> 
>       template<class CastFrom, class CastType, class Direction =
lua_to_cpp>
>       struct cast_to
>       {
>             template<class T>
>             T apply(lua_State *L, by_value<T> data, int index)
>             {
>                   typedef typename find_conversion_policy<1,
detail::null_type>::type converter_policy;
>                   typename mpl::apply_wrap2<converter_policy,
CastFrom, lua_to_cpp>::type converter;
> 
>                   return CastType::apply<CastFrom,
T>(converter.apply(L, LUABIND_DECORATE_TYPE(CastFrom), index));
>             }
> 
>             template<class T>
>             static int match(lua_State* L, by_value<T>, int index)
>             {
>                   typedef typename find_conversion_policy<1,
detail::null_type>::type converter_policy;
>                   typename mpl::apply_wrap2<converter_policy,
CastFrom, lua_to_cpp>::type converter;
> 
>                   return converter.match(L,
LUABIND_DECORATE_TYPE(CastFrom), index);
>             }
> 
>             template<class T>
>             void converter_postcall(lua_State*, T, int) {}
>       };
> 
>       template<int N, class CastFrom, class CastType>
>       struct cast_policy : conversion_policy<N>
>       {
>             struct only_accepts_values {};
>             struct only_converts_from_lua_to_cpp {};
> 
>             static void precall(lua_State*, const index_map&) {}
>             static void postcall(lua_State*, const index_map&) {}
> 
>             template<class T, class Direction>
>             struct apply
>             {
>                   //typedef reinterpret_cast_to<CastFrom, Direction>
type;
> 
>                   typedef typename
boost::mpl::if_<boost::is_same<Direction, lua_to_cpp>
>                         , typename
boost::mpl::if_<boost::is_pointer<T>
>                               , only_accepts_values
>                               , typename
boost::mpl::if_<boost::is_reference<T>
>                                     , only_accepts_values
>                                     , cast_to<CastFrom, CastType,
Direction> >::type>::type
>                         , only_converts_from_lua_to_cpp>::type type;
>             };
>       };
> }}
> 
> namespace luabind
> {
>       struct raw_c
>       {
>             template<class From, class To>
>             static To apply(From data)
>             {
>                   return (To)data;
>             }
>       };
> 
>       struct static_c
>       {
>             template<class From, class To>
>             static To apply(From data)
>             {
>                   return static_cast<To>(data);
>             }
>       };
> 
>       struct dynamic_c
>       {
>             template<class From, class To>
>             static To apply(From data)
>             {
>                   return dynamic_cast<To>(data);
>             }
>       };
> 
>       struct reinterpret_c
>       {
>             template<class From, class To>
>             static To apply(From data)
>             {
>                   return reinterpret_cast<To>(data);
>             }
>       };
> 
>       template<class CastFrom, class CastType, int N>
>       detail::policy_cons<detail::cast_policy<N, CastFrom, CastType>,
detail::null_type> 
>       cast(LUABIND_PLACEHOLDER_ARG(N)) 
>       { 
>             return detail::policy_cons<detail::cast_policy<N,
CastFrom, CastType>, detail::null_type>(); 
>       }
> }
> 
> #endif // LUABIND_REINTERPRET_CAST_POLICY_HPP_INCLUDED
> 
> 
> Any comments/questions, let me know!
> 
> Dan.
> 
>
------------------------------------------------------------------------
-
> This SF.net email is sponsored by the 2008 JavaOne(SM) Conference 
> Don't miss this year's exciting event. There's still time to save
$100. 
> Use priority code J8TL2D2. 
>
http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/j
avaone
> _______________________________________________
> luabind-user mailing list
> lua...@li...
> https://lists.sourceforge.net/lists/listinfo/luabind-user

________________________________

Hotmail on your mobile. Never miss another e-mail with
<http://www.livelife.ninemsn.com.au/article.aspx?id=343869>