Re: binding a c++ unary_function to lua

[Vyacheslav Egorov <mraleph@...>]

Panagiotis Vossos wrote:
> Is there any easy way to make it available to lua as a normal function?
>   
I think __call metamethod is what you are seeking.

Some untested and dirty (requires closure per functor and copy 
constructor) code:

template<typename T>
int trampoline(lua_State *L) { 
   T *self = (T*)lua_touserdata(L, 1);

   lua_remove(L, 1); // i am not sure that under normal circumstances 
such removal is safe,
                     // i.e. f will not be GCed during execution,
                     // so I am doing a little trick with upvalues   
  
   return self->operator() (L);
}

template<typename T>
T *pushfunctor(lua_State *L, const T& f) {

 T* p = (T*)lua_newuserdata(L, sizeof(T)); // stack: u ]
 new (p) T(f);

 lua_newtable(L);                         // stack: u t ]
 lua_pushvalue(L, -2);                    // stack: u t u ]
 lua_pushcclosure(L, &trampoline<T>, 1);  // stack: u t f ]
 lua_setfield(L, -2, "__call");           // stack: u t ]
 lua_setmetatable(L, -2);                 // stack: u ]

 return p;
}

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e.v.e