ceph/src/boost/libs/contract/example/features/optional_result_virtual.cpp

   1
   2 // Copyright (C) 2008-2018 Lorenzo Caminiti
   3 // Distributed under the Boost Software License, Version 1.0 (see accompanying
   4 // file LICENSE_1_0.txt or a copy at http://www.boost.org/LICENSE_1_0.txt).
   5 // See: http://www.boost.org/doc/libs/release/libs/contract/doc/html/index.html
   6
   7 #include <boost/contract.hpp>
   8 #include <boost/optional.hpp>
   9 #include <vector>
  10 #include <cassert>
  11
  12 template<typename T>
  13 class accessible {
  14 public:
  15     virtual T& at(unsigned index, boost::contract::virtual_* v = 0) = 0;
  16
  17     // Could program class invariants and contracts for following too.
  18     virtual T const& operator[](unsigned index) const = 0;
  19     virtual unsigned size() const = 0;
  20 };
  21
  22 //[optional_result_virtual
  23 template<typename T>
  24 T& accessible<T>::at(unsigned index, boost::contract::virtual_* v) {
  25     boost::optional<T&> result;
  26     // Pass `result` right after `v`...
  27     boost::contract::check c = boost::contract::public_function(v, result, this)
  28         .precondition([&] {
  29             BOOST_CONTRACT_ASSERT(index < size());
  30         })
  31         // ...plus postconditions take `result` as a parameter (not capture).
  32         .postcondition([&] (boost::optional<T const&> const& result) {
  33             BOOST_CONTRACT_ASSERT(*result == operator[](index));
  34         })
  35     ;
  36
  37     assert(false);
  38     return *result;
  39 }
  40 //]
  41
  42 template<typename T>
  43 class vector
  44     #define BASES public accessible<T>
  45     : BASES
  46 {
  47 public:
  48     typedef BOOST_CONTRACT_BASE_TYPES(BASES) base_types;
  49     #undef BASES
  50
  51     T& at(unsigned index, boost::contract::virtual_* v = 0) /* override */ {
  52         boost::optional<T&> result;
  53         // Pass `result` right after `v`...
  54         boost::contract::check c = boost::contract::public_function<
  55                 override_at>(v, result, &vector::at, this, index)
  56             // ...plus postconditions take `result` as parameter (not capture).
  57             .postcondition([&] (boost::optional<T const&> const& result) {
  58                 if(index == 0) BOOST_CONTRACT_ASSERT(*result == front());
  59             })
  60         ;
  61
  62         return *(result = vect_[index]);
  63     }
  64
  65     // Could program class invariants and contracts for following too.
  66     T const& operator[](unsigned index) const { return vect_[index]; }
  67     unsigned size() const { return vect_.size(); }
  68     T const& front() const { return vect_.front(); }
  69     void push_back(T const& value) { vect_.push_back(value); }
  70
  71     BOOST_CONTRACT_OVERRIDE(at)
  72
  73 private:
  74     std::vector<T> vect_;
  75 };
  76
  77 int main() {
  78     vector<int> v;
  79     v.push_back(123);
  80     v.push_back(456);
  81     v.push_back(789);
  82     int& x = v.at(1);
  83     assert(x == 456);
  84     x = -456;
  85     assert(v.at(1) == -456);
  86     return 0;
  87 }
  88