On 04/28/2010 10:45 AM, Joseph Gauterin wrote:
You're not missing anything - a lot of boost/std/std::tr1 is designed to be used with templates rather than runtime polymorphism - mixing the two isn't trivial.
I had a long and careful think about this, and my program design, and which of the two approaches might actually be more appropriate. It turns out that, contra my assumptions, a template approach works well -- it means some changes in the design/philosophy of the classes I'm building, but I think on balance they are positive changes. I tried the type erasure method and ran into two problems with it. The first was that the underlying random number generator isn't itself updated when runtime_generator is called, despite the use of references. If you do, mt19937 rng; runtime_generator<uint32_t> rng1(rng); for(int i=0;i!=10;++i) cout << uniform_real<double> (0.0,1.0) (rng1) << " "; cout << endl; runtime_generator<uint32_t> rng2(rng); for(int i=0;i!=10;++i) cout << uniform_real<double> (0.0,1.0) (rng2) << " "; cout << endl; ... you'll get the same sequence of 10 numbers. The second factor is that type erasure seems dodgy when not all the random number generators have the same return_type, and this can cause problems. For example, if you replace the mt19937 in the code above with a lagged_fibonacci607, it will just generate a series of zeros, because the lagged_fibonacci's return type is a double in [0,1). The "obvious" thing to do is just to use runtime_generator<double> but that has its own problems, because then e.g. the uniform_int distribution won't work with it. In summary, the risk of making buggered code seems quite high, so it seems the better option to either use the Boost random number generators with templated code, or to use an alternative that supports runtime polymorphism naturally, like GSL. Thanks once again for all the advice and assistance. It was very informative and I learned quite a bit from following up on the suggestions provided. Final question -- what is the appropriate way to save the state of a Boost random number generator so that another one can be seeded to take exactly the same state? Best wishes, -- Joe