ceph/src/boost/libs/hana/benchmark/fold_left/compile.cexpr.recursive.erb.cpp

   1 // Copyright Louis Dionne 2013-2016
   2 // Distributed under the Boost Software License, Version 1.0.
   3 // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
   4
   5 template <typename ...xs>
   6 struct list { };
   7
   8 template <typename T>
   9 struct basic_type { using type = T; };
  10
  11 template <typename T>
  12 constexpr basic_type<T> type{};
  13
  14
  15 template <typename x, typename ...xs>
  16 constexpr auto head(list<x, xs...>)
  17 { return type<x>; }
  18
  19 template <typename x, typename ...xs>
  20 constexpr auto tail(list<x, xs...>)
  21 { return list<xs...>{}; }
  22
  23 template <typename F, typename State, typename X, typename ...Xs>
  24 constexpr auto foldl(F f, State s, list<X, Xs...> xs)
  25 { return foldl(f, f(s, head(xs)), tail(xs)); }
  26
  27 template <typename F, typename State>
  28 constexpr auto foldl(F, State s, list<>)
  29 { return s; }
  30
  31 //////////////////////////////////////////////////////////////////////////////
  32
  33
  34 struct f {
  35     template <typename ...>
  36     struct result { };
  37
  38     template <typename X, typename Y>
  39     constexpr auto operator()(X, Y) const
  40     { return result<X, Y>{}; }
  41 };
  42
  43 template <int> struct x { };
  44 struct state { };
  45
  46 int main() {
  47     constexpr auto xs = list<
  48         <%= (1..input_size).map { |i| "x<#{i}>" }.join(', ') %>
  49     >{};
  50
  51     constexpr auto result = foldl(f{}, state{}, xs);
  52     (void)result;
  53 }