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

From: Andy (atompkins_at_[hidden])
Date: 2007-06-13 16:47:35

"Jos Hickson" <jos.hickson_at_[hidden]> wrote in
news:fc03d05a0706120226n717d457fueca21627444a90d3_at_[hidden]: 

< snip >

>> 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 >

>> >
>> > 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;