ceph/src/boost/libs/functional/hash/examples/portable.cpp

   1
   2 // Copyright 2005-2009 Daniel James.
   3 // Distributed under the Boost Software License, Version 1.0. (See accompanying
   4 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   5
   6 // Force use of assert.
   7 #if defined(NDEBUG)
   8 #undef NDEBUG
   9 #endif
  10
  11 #include <boost/functional/hash.hpp>
  12 #include <cassert>
  13
  14 // This example illustrates how to customise boost::hash portably, so that
  15 // it'll work on both compilers that don't implement argument dependent lookup
  16 // and compilers that implement strict two-phase template instantiation.
  17
  18 namespace foo
  19 {
  20     template <class T>
  21     class custom_type
  22     {
  23         T value;
  24     public:
  25         custom_type(T x) : value(x) {}
  26
  27         std::size_t hash() const
  28         {
  29             boost::hash<T> hasher;
  30             return hasher(value);
  31         }
  32     };
  33 }
  34
  35 #ifdef BOOST_NO_ARGUMENT_DEPENDENT_LOOKUP
  36 namespace boost
  37 #else
  38 namespace foo
  39 #endif
  40 {
  41     template <class T>
  42     std::size_t hash_value(foo::custom_type<T> x)
  43     {
  44         return x.hash();
  45     }
  46 }
  47
  48 int main()
  49 {
  50     foo::custom_type<int> x(1), y(2), z(1);
  51
  52     boost::hash<foo::custom_type<int> > hasher;
  53
  54     assert(hasher(x) == hasher(x));
  55     assert(hasher(x) != hasher(y));
  56     assert(hasher(x) == hasher(z));
  57
  58     return 0;
  59 }