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

   1 /*=============================================================================
   2     Copyright (c) 2017 Paul Fultz II
   3     in.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     in.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 #ifdef _MSC_VER
  19 template<class R, class T>
  20 auto member_find(const R& r, const T& x) BOOST_HOF_RETURNS(r.find(x));
  21 #endif
  22
  23 // Function to find an iterator using a containers built-in find if available
  24 BOOST_HOF_STATIC_LAMBDA_FUNCTION(find_iterator) = first_of(
  25     [](const std::string& s, const auto& x)
  26     {
  27         auto index = s.find(x);
  28         if (index == std::string::npos) return s.end();
  29         else return s.begin() + index;
  30     },
  31 #ifdef _MSC_VER
  32     // On MSVC, trailing decltype doesn't work with generic lambdas, so a
  33     // seperate function can be used instead.
  34     BOOST_HOF_LIFT(member_find),
  35 #else
  36     [](const auto& r, const auto& x) BOOST_HOF_RETURNS(r.find(x)),
  37 #endif
  38     [](const auto& r, const auto& x)
  39     {
  40         using std::begin;
  41         using std::end;
  42         return std::find(begin(r), end(r), x);
  43     }
  44 );
  45 // Implement an infix `in` operator to check if a range contains an element
  46 BOOST_HOF_STATIC_LAMBDA_FUNCTION(in) = infix(
  47     [](const auto& x, const auto& r)
  48     {
  49         using std::end;
  50         return find_iterator(r, x) != end(r);
  51     }
  52 );
  53 // Negate version of `in`
  54 BOOST_HOF_STATIC_LAMBDA_FUNCTION(not_in) = infix(compose(not _, in));
  55
  56 int main()
  57 {
  58     // Check if vector contains element
  59     std::vector<int> numbers = { 1, 2, 3, 4, 5 };
  60     if (5 <in> numbers) std::cout << "Yes" << std::endl;
  61
  62     // Check if string contains element
  63     std::string s = "hello world";
  64     if ("hello" <in> s) std::cout << "Yes" << std::endl;
  65
  66     // Check if map contains element
  67     std::map<int, std::string> number_map = {
  68         { 1, "1" },
  69         { 2, "2" },
  70         { 3, "3" },
  71         { 4, "4" }
  72     };
  73
  74     if (4 <in> number_map) std::cout << "Yes" << std::endl;
  75
  76     // Check if map doesn't contains element
  77     if (not (8 <in> numbers)) std::cout << "No" << std::endl;
  78     if (8 <not_in> numbers) std::cout << "No" << std::endl;
  79
  80 }
  81