Re: [Boost-users] [random]how to initialise a rng for use in the initialiser list?

Subject: Re: [Boost-users] [random]how to initialise a rng for use in the initialiser list?
From: François Mauger (mauger_at_[hidden])
Date: 2008-11-22 05:21:31

Hi

For this kind of stuff, when complex objects have strong
interrelationships at startup,
I prefer usually to "delay" (not the proper word, I guess)
the initiliazation of material within the class in this way:

>>>
class my_class
{
private:
  long     __seed; // I always keep tracks of the seed I use in RNPG stuff
  rng_t *  __rng; // note here i use a dynamically allocated instance
  matrix_t __matrix // could do the same here but it depends on the pb...

  rng_t & rng ()
  {
     if ( __rng == 0) throw "Ooops!";
     return *__rng;
  }

  void initialise ()
  {
    // do something useful using 'rng ()'...
  }

  void __init ()
  {
    __rng = new my_rng_t (__seed);
    // do whatever initialization you need here...
    __matrix.initialise ();

    // more init...
  }

  void __del ()
  {
    if (__rng != 0) delete __rng;
    __rng = 0;

    // clean other stuff...
  }

public:
  my_class (long seed_) : __rng (0) //, __matrix (DEFAULT CTOR PARAMETERS)
  {
     __seed = seed_;
     __rng = 0;
     __init ();
  }

  ~my_class ()
  {
     __del ();
  }

  ...
};
<<<

But it is matter of preference...
and maybe you don't want to use dyn. alloc. for the '__rng' field.
It also enables to reuse this kind of object using proper
public "reset ()" and "init (long?)" methods...
Using some 'rng_t' virtual base PRNG class (if available)
allows you to easily allocate another kind of generator...

Hope it can help.

regards

frc
--
Francois Mauger
Laboratoire de Physique Corpusculaire de Caen et Universite de Caen
ENSICAEN - 6, Boulevard du Marechal Juin, 14050 CAEN Cedex, FRANCE
e-mail: mauger_at_[hidden]
> Moritz Beber wrote:
>>
>> I use a class which keeps the random number generator around as a member
>> variable; this class also has a const matrix. Now in the constructor of
>> the class I do something like:
>>
>> my_class::my_class(args) : rng(seed), matrix(initialise()), ...
>> {
>> 	...
>> }
>>
>> Of course, I want to use the rng to initialise the matrix and that's
>> where things fail. I guess, I could use a different rng just to fill the
>> matrix, or make it non-const and fill it in the constructor body. But
>> does anyone know a neat trick to do this in the way proposed?
>>
>>
>
> This might not be the best way, but you need to at least ensure that the
> rng member of the class is declared before the matrix (in the class
> declaration.)
>
> Sorry if this doesn't, in fact, answer you problem.
> -yzt
>
>
>
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