C++ FRUG 07/04/2016

frug.cpp

#include <initializer_list>
#include <functional>
#include <iostream>
#include <utility>
#include <tuple>

//--------------------------------------------------------
// Appliquer une fonction sur une ligne d'arguments
template<class F, class...Ts> F for_each_args(F f, Ts&&...a)
{
  return (void)std::initializer_list<int>{((void)std::ref(f)(std::forward<Ts>(a)),0)...}, f;
}

//--------------------------------------------------------
// Appliquer une fonction sur chaque membres d'un tuple
namespace detail 
{
  template <class F, class Tuple, std::size_t... I>
  decltype(auto) apply_impl( F&& f, Tuple&& t, std::index_sequence<I...> )
  {
    return std::forward<F>(f)(std::get<I>(std::forward<Tuple>(t))...);
  }
}
 
template <class F, class Tuple> decltype(auto) apply(F&& f, Tuple&& t)
{
    return detail::apply_impl(std::forward<F>(f), std::forward<Tuple>(t),
        std::make_index_sequence<std::tuple_size<std::decay_t<Tuple>>{}>{});
}

//--------------------------------------------------------
// Une reduction sans recursion
namespace detail 
{
  template <class Array, std::size_t... I>
  decltype(auto) reduce_impl( Array const& a, std::index_sequence<I...> )
  {
    using type = typename Array::value_type;
    type r{};
    
    (void)std::initializer_list<type>{ (r+= a[I])... };
    
    return r;
  }
}
 
template<class Array> decltype(auto) reduce(Array const& a)
{
    return detail::reduce_impl(a, std::make_index_sequence<std::tuple_size<Array>{}>{});
}

//--------------------------------------------------------
template<bool... B> struct bools_ {}
;
// Reduction de meta-predicat
template<template<class> class Pred, typename... T>
struct all : std::is_same< bools_<true             , Pred<T>::value... >
                         , bools_<Pred<T>::value..., true              >
                         >
{};

//--------------------------------------------------------
int main()
{
  auto disp = [](auto x) { std::cout << x << " "; };
  for_each_args( disp, 1,"3",5.f,"rofl",39u );  
  std::cout << "\n";
  
  auto t = std::make_tuple(4,3.f,88u,'z');
  apply( [&](auto const&... x) { for_each_args( disp, x... );   } , t);
  std::cout << "\n";
  
  std::array<float,5> ff{1,2,3,4,5};
  std::cout << reduce(ff) << "\n";
  
  using is_all_pointer = all< std::is_pointer, char*, void**, float****>;
  std::cout << std::boolalpha << is_all_pointer::value << "\n";
  
  using almost_all_pointer = all< std::is_pointer, char*, void**, long, float****>;
  std::cout <<  std::boolalpha << almost_all_pointer::value << "\n";
}