libs/contract/example/features/move.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 <vector>
   9 #include <utility>
  10 #include <cassert>
  11
  12 //[move
  13 class circular_buffer :
  14         private boost::contract::constructor_precondition<circular_buffer> {
  15 public:
  16     void invariant() const {
  17         if(!moved()) { // Do not check (some) invariants for moved-from objects.
  18             BOOST_CONTRACT_ASSERT(index() < size());
  19         }
  20         // More invariants here that hold also for moved-from objects (e.g.,
  21         // all assertions necessary to successfully destroy moved-from objects).
  22     }
  23
  24     // Move constructor.
  25     circular_buffer(circular_buffer&& other) :
  26         boost::contract::constructor_precondition<circular_buffer>([&] {
  27             BOOST_CONTRACT_ASSERT(!other.moved());
  28         })
  29     {
  30         boost::contract::check c = boost::contract::constructor(this)
  31             .postcondition([&] {
  32                 BOOST_CONTRACT_ASSERT(!moved());
  33                 BOOST_CONTRACT_ASSERT(other.moved());
  34             })
  35         ;
  36
  37         move(std::forward<circular_buffer>(other));
  38     }
  39
  40     // Move assignment.
  41     circular_buffer& operator=(circular_buffer&& other) {
  42         // Moved-from can be (move) assigned (so no pre `!moved()` here).
  43         boost::contract::check c = boost::contract::public_function(this)
  44             .precondition([&] {
  45                 BOOST_CONTRACT_ASSERT(!other.moved());
  46             })
  47             .postcondition([&] {
  48                 BOOST_CONTRACT_ASSERT(!moved());
  49                 BOOST_CONTRACT_ASSERT(other.moved());
  50             })
  51         ;
  52
  53         return move(std::forward<circular_buffer>(other));
  54     }
  55
  56     ~circular_buffer() {
  57         // Moved-from can always be destroyed (in fact no preconditions).
  58         boost::contract::check c = boost::contract::destructor(this);
  59     }
  60
  61     bool moved() const {
  62         boost::contract::check c = boost::contract::public_function(this);
  63         return moved_;
  64     }
  65
  66 private:
  67     bool moved_;
  68
  69     /* ... */
  70 //]
  71
  72 public:
  73     explicit circular_buffer(std::vector<char> const& data,
  74             unsigned start = 0) :
  75         boost::contract::constructor_precondition<circular_buffer>([&] {
  76             BOOST_CONTRACT_ASSERT(start < data.size());
  77         }),
  78         moved_(false),
  79         data_(data),
  80         index_(start)
  81     {
  82         boost::contract::check c = boost::contract::constructor(this)
  83             .postcondition([&] {
  84                 BOOST_CONTRACT_ASSERT(!moved());
  85             })
  86         ;
  87     }
  88
  89     // Copy constructor.
  90     circular_buffer(circular_buffer const& other) :
  91         boost::contract::constructor_precondition<circular_buffer>([&] {
  92             BOOST_CONTRACT_ASSERT(!other.moved());
  93         })
  94     {
  95         boost::contract::check c = boost::contract::constructor(this)
  96             .postcondition([&] {
  97                 BOOST_CONTRACT_ASSERT(!moved());
  98             })
  99         ;
 100
 101         copy(other);
 102     }
 103
 104     // Copy assignment.
 105     circular_buffer& operator=(circular_buffer const& other) {
 106         // Moved-from can be (copy) assigned (so no pre `!moved()` here).
 107         boost::contract::check c = boost::contract::public_function(this)
 108             .precondition([&] {
 109                 BOOST_CONTRACT_ASSERT(!other.moved());
 110             })
 111             .postcondition([&] {
 112                 BOOST_CONTRACT_ASSERT(!moved());
 113             })
 114         ;
 115
 116         return copy(other);
 117     }
 118
 119     char read() {
 120         boost::contract::check c = boost::contract::public_function(this)
 121             .precondition([&] {
 122                 BOOST_CONTRACT_ASSERT(!moved());
 123             })
 124         ;
 125
 126         unsigned i = index_++;
 127         if(index_ == data_.size()) index_ = 0; // Circular.
 128         return data_.at(i);
 129     }
 130
 131 private:
 132     circular_buffer& copy(circular_buffer const& other) {
 133         data_ = other.data_;
 134         index_ = other.index_;
 135         moved_ = false;
 136         return *this;
 137     }
 138
 139     circular_buffer& move(circular_buffer&& other) {
 140         data_ = std::move(other.data_);
 141         index_ = std::move(other.index_);
 142         moved_ = false;
 143         other.moved_ = true; // Mark moved-from object.
 144         return *this;
 145     }
 146
 147     std::vector<char> data_;
 148     unsigned index_;
 149
 150 public:
 151     unsigned index() const {
 152         boost::contract::check c = boost::contract::public_function(this);
 153         return index_;
 154     }
 155
 156     unsigned size() const {
 157         boost::contract::check c = boost::contract::public_function(this);
 158         return data_.size();
 159     }
 160 };
 161
 162 int main() {
 163     struct err {};
 164     boost::contract::set_precondition_failure(
 165             [] (boost::contract::from) { throw err(); });
 166
 167     {
 168         circular_buffer x({'a', 'b', 'c', 'd'}, 2);
 169         assert(x.read() == 'c');
 170
 171         circular_buffer y1 = x; // Copy constructor.
 172         assert(y1.read() == 'd');
 173         assert(x.read() == 'd');
 174
 175         circular_buffer y2({'h'});
 176         y2 = x; // Copy assignment.
 177         assert(y2.read() == 'a');
 178         assert(x.read() == 'a');
 179
 180         circular_buffer z1 = std::move(x); // Move constructor.
 181         assert(z1.read() == 'b');
 182         // Calling `x.read()` would fail `!moved()` precondition.
 183
 184         x = y1; // Moved-from `x` can be copy assigned.
 185         assert(x.read() == 'a');
 186         assert(y1.read() == 'a');
 187
 188         circular_buffer z2({'k'});
 189         z2 = std::move(x); // Move assignment.
 190         assert(z2.read() == 'b');
 191         // Calling `x.read()` would fail `!moved()` precondition.
 192
 193         x = std::move(y2); // Moved-from `x` can be move assigned.
 194         assert(x.read() == 'b');
 195         // Calling `y2.read()` would fail `!moved()` precondition.
 196
 197     } // Moved-from `y2` can be destroyed.
 198
 199     return 0;
 200 }
 201