ceph/src/boost/libs/hof/example/static_if.cpp

   1 /*=============================================================================
   2     Copyright (c) 2017 Paul Fultz II
   3     static_if.cpp
   4     Distributed under the Boost Software License, Version 1.0. (See accompanying
   5     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6 ==============================================================================*/
   7 /*=============================================================================
   8     Copyright (c) 2016 Paul Fultz II
   9     static_if.cpp
  10     Distributed under the Boost Software License, Version 1.0. (See accompanying
  11     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  12 ==============================================================================*/
  13
  14 #include "example.h"
  15
  16 using namespace boost::hof;
  17
  18 // static_if example taken from Baptiste Wicht:
  19 // http://baptiste-wicht.com/posts/2015/07/simulate-static_if-with-c11c14.html
  20
  21 template<typename T>
  22 void decrement_kindof(T& value)
  23 {
  24     eval(first_of(
  25         if_(std::is_same<std::string, T>())([&](auto id){
  26             id(value).pop_back();
  27         }),
  28         [&](auto id){
  29             --id(value);
  30         }
  31     ));
  32 }
  33
  34 int main()
  35 {
  36     std::string s = "hello!";
  37     decrement_kindof(s);
  38     assert(s == "hello");
  39
  40     int i = 4;
  41     decrement_kindof(i);
  42     assert(i == 3);
  43 }