Re: [boost] [review] Boost.Guid

From: Andy (atompkins_at_[hidden])
Date: 2007-05-08 09:23:05

"Johan Nilsson" <r.johan.nilsson_at_[hidden]> wrote in
news:f1p510$eig$1_at_[hidden]: 

> Andy wrote:
>> "Peter Dimov" <pdimov_at_[hidden]> wrote in
>> news:002e01c790c0$0f2d3510$6407a80a_at_pdimov2:
>>
>>> Andy wrote:
>>>
>>>> I agree that the create function needs improvement.  It suffers
>>>> from threading problems (because of static variables) and from a
>>>> hard coded random number generator (also a hard coded seed).
>>>>
>>>> My solution is to create a generator class, as follows:
>>>>
>>>> // maybe a better name
>>>> // maybe a different default random number generator
>>>> template <typename UniformRandomNumberGenerator = boost::mt19937>
>>>> class random_guid_generator : boost::noncopyable
>>>
>>> [...]
>>>
>>>> random_guid_generator<> guid_gen;
>>>> guid g = guid_gen.create();
>>>
>>> Why not just add an Engine & e parameter to guid::create?
>>
>> Good idea.  Something like:
>>
>> template<typename Engine>
>> boost::guid guid::create(Engine& e = boost::mt19937(get_seed()));
> 
> [sorry for jumping in]
> 
> That would need to be "Engine const&", right?

Right.

> 
>>
>> where get_seed() does something like what you said below.
>>
>> I want to be able to call the create function with a default Engine
>> because I don't want to force users to create one themselves.
> 
> I'd suggest to rather use an overload of create with zero arguments.
> Helps if the methods are ever used with function binding.

Sure.

template <typename Engine>
boost::guid guid::create(Engine& engine)
{
  ...
}

boost::guid guid::create()
{
  boost::mt19937 engine(get_seed());
  return create(engine);
}

> 
>>  The
>> only downside is for people who do want a different engine/seed, they
>> will
>> have to pass that engine to the function everytime they call it.
> 
> Yes, people are likely to go for one specific engine within a specific
> context (e.g. application). Perhaps a _complementing_ guid_factory
> would be usable for people preferring the generator/factory interface
> you mentioned above.
> 
> template<typename Engine>
> class guid_factory{
> ...
> explicit guid_factory(Engine const& e = Engine())
>  : e_(e)
> {}
> 
> guid create_guid() [const?]
> {
>     return guid::create(e_);
> }
> ...
> [mutable?] Engine e_;
> };
> 
> 
> / Johan
> 

Good idea. Provide both.

Andy.