Range adaptor for adjacent_difference

25 Aug 2005

      (Resending to the Boost distribution list.)

I have a suggestion for the range_ex library.  It is such a useful library -- 
IMHO, the Boost.Range library is useless without it.  I would also like to 
see it include a numeric.hpp that has a version of adjacent_difference, etc.  
In my mind, any standard algorithm that takes an input iterator and an output 
iterator as parameters could be rewritten as a range adaptor.  I attached a 
sample implementation.  It's not done using Boost coding standards or 
anything.  BTW, I also found the "tail" (a.k.a. "pop_front") adaptor to be 
useful in conjunction with adjacent_difference.  Here's how I use it in my 
toy project:

    QuoteSum sum(
        accumulate(
            make_ResUse_range(result) |
                boost::adaptor::transform(
                    boost::bind(adaptable_constructor<QuoteAddend>(),
                        boost::bind(&parseTimestampColumn,
                            boost::bind(&mysqlpp::Row::operator[], _1,
0)
                        ),
                        boost::bind(&mysqlpp::Row::operator[], _1, 1)
                    )
                ) |
                adjacent_difference() |
                tail(),
            QuoteSum(),
            AccumulateQuotes(inverseYearDuration, annualMeanRate)
        )
    );

Thanks for the work that went into the library -- I hope it gets adopted.  I 
personally find it much more powerful than BOOST_FOREACH.

-- chad

Chad Parry

Eric Niebler

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