simple example of a fusion style rtim of a tuple.

rtrim_example

namespace detail
{
  //create a Factory item with only the first N items in it
template< template<class ...> class Factory,
          int TruncateSize,
          int ItemsToDrop,
          class T,
          class ...OtherArgs>
struct rtrim
{
  typedef typename rtrim<Factory,TruncateSize,ItemsToDrop-1,OtherArgs...,T>::type type;

  type operator()(T t, OtherArgs... args) const
  {
    return rtrim<Factory,TruncateSize,ItemsToDrop-1,OtherArgs...,T>()(args...,t);
  }
};

//create a Factory item with only the first N items in it
template<template<class ...> class Factory, int TruncateSize, class T, class ...OtherArgs>
struct rtrim<Factory, TruncateSize, 0, T, OtherArgs...>
{
  enum{M = sizeof...(OtherArgs) - TruncateSize};
  typedef typename ltrim<Factory,M,OtherArgs...,T>::type type;

  type operator()(T t, OtherArgs... args) const
  {
    return ltrim<Factory,M,OtherArgs...,T>()(args...,t);
  }
};

}

//create a Factory item with only the first N items in it, aka rtrim
template< template<class ...> class Factory,
          int TruncateSize,
          class T,
          class ...OtherArgs>
struct rtrim
{
  typedef typename detail::rtrim<Factory,TruncateSize,TruncateSize-1,OtherArgs...,T>::type type;

  type operator()(T t, OtherArgs... args) const
  {
    return detail::rtrim<Factory,TruncateSize,TruncateSize-1,OtherArgs...,T>()(args...,t);
  }
};