Re: [Boost-users] total noob help: LAMBDA with zip_iterator

8 Apr 2006


      alright i am trying to stimulate the safety algorithm Operating system
concepts seventh edition book. Note i haven't use static_assert yet.
Basically i am trying to experiment on how boost can help replace low level
concept code in which any language be it, php, perl, java (i.e. replace of
indexing if possible) can write simple algorithm whether to increase
readability, maintainbility or anything. All these are just experimental
code. Thank you very much.The problem with python iterators is that you
can't reassign iteration values in list.

template 
struct DimArray
{
    typedef typename boost::multi_array ndimarr;
    typedef typename boost::multi_array::size_type size;
};

   /******************************************************
    * check to see if the current status is safe         *
    * @return true if state is safe and false otherwise  *
    * @param Max is n x m matrix of maximum resources    *
    * @param Alloc is n x m matrix of allocated resources*
    * @param Need is n x m matrix of needed resources    *
    * @param Available is m size avaliable resource vec  *
    * @templateparam: T any numeric type (int, double, float)     *
    * @templateparam: CONT any container type of std::allocator *
    *****************************************************/
template 
           class CONT
...
bool DLA::isSafe(const typename DimArray::ndimarr& MAX,
               const typename DimArray::ndimarr& Alloc,
               const typename DimArray::ndimarr& Need,
               const typename DimArray::ndimarr& Available)
{
    using namespace boost::lambda;
   BOOST_STATIC_ASSERT(boost::is_integral<T>::value);
    typename DimArray::ndimarr Work(Available);
    typedef typename DimArray::size TDS;
    const TDS outer_sz(MAX.size());
    CONT<bool> Finish(outer_sz, false);
    typedef typename CONT<bool>::const_iterator ContIter;
    typedef typename DimArray::ndimarr::const_iterator MultIter;
    typedef typename DimArray::ndimarr::const_iterator OneIter;
    ContIter iter;
 MultIter beg1(Need.begin());
    MultIter beg2(Alloc.begin());
    MultIter end1(Need.end());
    MultIter end2(Alloc.end());
 ContIter beg3(Finish.begin());
 ContIter end3(Finish.end());
    TDS ind(0);
    while ((iter = std::find(Finish.begin(), Finish.end(), false)) !=
Finish.end())
    {
  /*
    new code
  std::for_each(
           // iterate through (Need, Alloc, Finish).
            boost::make_zip_iterator(boost::make_tuple(beg1, beg2, beg3)),
            boost::make_zip_iterator(boost::make_tuple(end1, end2, end3)),
           (
               Parts where i wish to use lambda for abstraction .
                Assume:
                  _1 = Need[i],
                  _2 = Alloc[i],
                  _3 = Finish[i],
                 if (_1 == false && _3 <= Work)
                {
                        _3 = true;
                        Work += _2;
                 }
             ++var(ind)
          )
    );
   */
   /*
    Old code
     for (int i = distance(Finish.begin(), iter); i < Finish.size(); ++i)
          {
              if (Finish[i] == false && ((typename DimArray::ndimarr)
Need[i]) <= Work)
              {
                 Finish[i] = true;
                 Work = array_add<T>(Work, ((typename DimArray::ndimarr)Alloc[i]));
                 std::cout << "p[" << i << "]\n";
              }
          }
      */
    }
    return (std::binary_search(Finish.begin(), Finish.end(), false))
          ? false : true;
}


On 4/7/06, David Abrahams  wrote:
...
"chun ping wang"  writes:
...
I have several questions that I asked earlier but never got an answer.
So I will start one by one..
a.) How do I use lambda with zip_iterator.  (assuming you have a
zip_iterator of vector, list, map)?
Thats my first question...
There are many possible answers.  What are you trying to accomplish
with lambda and zip_iterator?
--
Dave Abrahams
Boost Consulting
www.boost-consulting.com
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