ceph/src/boost/libs/local_function/example/phoenix_factorial.cpp

   1
   2 // Copyright (C) 2009-2012 Lorenzo Caminiti
   3 // Distributed under the Boost Software License, Version 1.0
   4 // (see accompanying file LICENSE_1_0.txt or a copy at
   5 // http://www.boost.org/LICENSE_1_0.txt)
   6 // Home at http://www.boost.org/libs/local_function
   7
   8 #include <boost/phoenix/core.hpp>
   9 #include <boost/phoenix/function.hpp>
  10 #include <boost/detail/lightweight_test.hpp>
  11
  12 //[phoenix_factorial
  13 struct factorial_impl { // Phoenix function from global functor.
  14     template<typename Sig>
  15     struct result;
  16
  17     template<typename This, typename Arg>
  18     struct result<This (Arg)> : result<This (Arg const&)> {};
  19
  20     template<typename This, typename Arg>
  21     struct result<This (Arg&)> { typedef Arg type; };
  22
  23     template<typename Arg> // Polymorphic.
  24     Arg operator()(Arg n) const {
  25         return (n <= 0) ? 1 : n * (*this)(n - 1);
  26     }
  27 };
  28
  29 int main(void) {
  30     using boost::phoenix::arg_names::arg1;
  31
  32     boost::phoenix::function<factorial_impl> factorial;
  33
  34     int i = 4;
  35     BOOST_TEST(factorial(i)() == 24);      // Call.
  36     BOOST_TEST(factorial(arg1)(i) == 24);  // Lazy call.
  37     return boost::report_errors();
  38 }
  39 //]
  40