How to iterate over a boost::fusion sequence? - c++

Question

I'm trying to initialise a list of args to use with fusion::invoke.
The args are all of the form:
template <typename Type>
struct ArgWrapper
{
inline ArgWrapper(){}
inline void Setup(lua_State*L,int idx)
{
//setup this value from the lua state...
//in reality this class is specialised for different lua types
}
operator Type(){return value;}
Type value;
};
So I can do, for example
int add(int a,int b){return a+b;}
fusion::vector<ArgsWrapper<int>,ArgsWrapper<int> > v;
fusion::at_c<0>(v).value=1;
fusion::at_c<1>(v).value=2;
std::cout<<fusion::invoke(add,v)//prints 3
But if I have a fusion sequence of type FusionListType, where I know each type in the sequence is an ArgWrapper of some type, how can I iterate through that list and call the Setup function on each element (I have just one lua_State pointer and want to use it as the first argument for Setup, and I want to use the position in the sequence as the second argument).
So for a vector of size 3 I want the resultant logic to be:
lua_State*L;
fusion::at_c<0>.Setup(L,1);
fusion::at_c<1>.Setup(L,2);
fusion::at_c<2>.Setup(L,3);
I have tried:
template<typename ArgWrapperType,int N>
void FillArgWrapper(ArgWrapperType arg,lua_State*L)
{
fusion::at_c<N>(arg).Setup(L,N+1);
}
template<typename ArgWrapperType>
void FillArgWrapper<ArgWrapperType,0>(ArgWrapperType arg,lua_State*L)
{
fusion::at_c<0>(arg).Setup(L,1);
}
But this fails to compile, saying function template partial specialisation ‘FillArgWrapper<ArgWrapperType, 0>’ is not allowed.
Thanks in advance.

Answer 1

Ok, I figured it out. I need to be using a struct:
template <typename ArgWrapperList,u32 N=mpl::size<ArgWrapperList>::value-1>
struct ArgWrapperListFiller
{
static inline void Setup(ArgWrapperList &args,lua_State*L)
{
fusion::at_c<N>(args).Setup(L,N+1);
ArgWrapperListFiller<ArgWrapperList,N-1>::Setup(args,L);
}
};
template <typename ArgWrapperList> //base case, do not recurse
struct ArgWrapperListFiller<ArgWrapperList,0>
{
static inline void Fill(ArgWrapperList &args,lua_State*L)
{
fusion::at_c<0>(args).Setup(L,1);
};
};