Re: [Boost-users] [Random] Passing an arbitrary uniform random number generator to a function

Subject: Re: [Boost-users] [Random] Passing an arbitrary uniform random number generator to a function
From: John Dlugosz (JDlugosz_at_[hidden])
Date: 2010-04-28 11:29:12

Your mention of "you need type erasure" makes me think of using boost::function to do the job, which I suppose could replace the explicit writing of the runtime_generator class.  But still, nice idea to wrap the virtual function taking the wrapped thing with a non-virtual template member that does the wrapping.

> -----Original Message-----
> From: boost-users-bounces_at_[hidden] [mailto:boost-users-
> bounces_at_[hidden]] On Behalf Of Joseph Gauterin
> Sent: Tuesday, April 27, 2010 6:50 AM
> To: boost-users_at_[hidden]
> Subject: Re: [Boost-users] [Random] Passing an arbitrary uniform random
> number generator to a function
> 
> Looks like you need some sort of type erasure (Steve's suggestion uses
> boost::function for that):
> 
> * Create a class that can be passed to uniform_real as a generator -
> that is what Steve's runtime_generator class is for.
> * Give runtime_generator a constructor that takes a single argument of
> a template type, initialize min_ and max_ from that and store the
> argument in impl (that will compile if the argument is a rng that
> follows the correct conventions)
> * Write the virtual function you wanted taking an argument of type
> runtime_generator<double>& - but make it private
> * Write a non-virtual public template function to wrap the rng
> 
> It's difficult to explain concisely - here's what the code should look
> like (untested - just for explanation):
> 
> template<class ResultType>
> class runtime_generator {
> public:
> 
>   template <class T>
>   explicit runtime_generator(T& rng)
>     : min_(rng.min()), max_(rng.max()), impl(rng) {
>   }
> 
>   ResultType min() const { return min_; }
>   ResultType max() const { return max_; }
>   ResultType operator()() { return impl(); }
> 
> private:
>   ResultType min_, max_;
>   boost::function<ResultType()> impl;
> };
> 
> 
> //in your class...
> public:
> template<class rng_t>
> double foo(rng_t& urng)
> {
>   runtime_generator<double> rtRNG(urng);
>   return foo_(rtRNG);
> }
> 
> private:
> virtual double foo_(runtime_generator<double> &urng)
> {
>   double x = uniform_real<double> (0.0, 10.0) (urng);
>   double y = uniform_real<double> (5.0, 7.0) (urng);
>   return (x*y);
> }
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