Re: [boost] [uuid] uuid::create() function

13 Jun 2007

      "Jos Hickson" <jos.hickson@gmail.com> wrote in
news:fc03d05a0706120226n717d457fueca21627444a90d3@mail.gmail.com: 

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Really what we need is a Boost.Seed library to compliment
Boost.Random so that anybody like yourself using the latter doesn't
have to spend all this time wondering how to seed things generically.
I think that the seed class would be a good addition to Boost.Random.

< snip >
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template <typename Engine=boost::mt19937>
class uuid_generator {
public:
  uuid_generator() {
    boost::seed_rgn e;
    boost::generator_iterator<boost::seed_rng> begin(&e);
    boost::generator_iterator<boost::seed_rnd> end;
    en_.seed(begin, end);
  }
boost::uuid operator()() {
    // get random data from en_
    // return uuid based on this data
  }
private:
  Engine en_;
};
Now this works fine, the slow seed_rng is used to fully seed the
random number generator used.  It can be specialized for
boost::random_device since boost::random_device does not have a
seed function.
Andy.
So now I have this, and I like it, but I have been unable to use 
boost::enable_if, and boost::disable_if to enable/disable the constructors.
template <typename Engine = boost::mt19937>
class basic_uuid_generator {
public:

  // only enable if engine can not be seeded
  // boost::random_device does not need seeding
  basic_uuid_generator(/*enable only if Engine=boost::random_device*/)
  {}

  // enable if engine can be seeded
  // seed engine
  basic_uuid_generator(/*enable if Engine != boost::random_device*/)
  {
    boost::seed_rgn seed;
    boost::generator_iterator<boost::seed_rng> begin(&seed);
    boost::generator_iterator<boost::seed_rng> end;
    en_.seed(begin, end);
  }

  // assume they have already seeded e and make a copy
  // maybe we should store a reference to e?
  explicit uuid_generator(Engine const& e)
    : en_(e)
  {}

  boost::uuid operator()() { ... }

priavte:
  Engine en_;
};

typedef basic_uuid_generator<> uuid_generator;