[boost] Re: www.boost.org updated

From: Nathan Myers (ncm_at_[hidden])
Date: 1998-12-06 17:20:50

Beman Dawes writes:
 > The background on the above is that when Greg looked at my min_rand
 > class, he commented that it was very close to being useful as an STL
 > compliant input iterator.
 > 
 > I tried to work that out, but got hung up on termination.  For
 > example, if you wanted 1000 random numbers in a vector, you could
 > write something like:
 > 
 >    min_rand rng;
 >    vector<long> vec( rng, ??? );  // oops! no way to specify end
 >                
 > A third container-like class is needed, I think.  end() would return
 > 0,
 > begin() would return an iterator with operator++() which returned
 > ++rng for 1000 calls, then returned 0:
 > 
 >    min_rand rng;
 >    iter_counter itrc( rng, 1000 );
 >    vector<long> vec( itrc.begin(), itrc.end() );
 > 
 > Anyhow, that is the problem Greg is thinking about.

That seems like extra apparatus.  It's not a container.
Just define operator+ for it.

 >    min_rand rng;
 >    iter_counter itrc( rng );
 >    vector<long> vec( itrc, itrc + 1000 );

You compute *itrc lazily, so if you never say *(itrc + 1000),
you don't have to compute all the random numbers in between.

But even this seems like more stuff than is needed.
A better way might be to have a "singular value", as for 
stream iterators.  Then:

  vector<long> vec( iter_counter(min_rand(), 1000), 
                    iter_counter() );

The singular value compares equal to any iter_counter that 
is past the end of its range.

Nathan Myers
ncm_at_[hidden]
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