Re: [Boost-users] [iterator] make_zip_iterator

From: Robert Ramey (ramey_at_[hidden])
Date: 2007-02-17 19:34:42

Well, I would like to take this opportunity to plug "dataflow iterators" 
which is part of the serialization library.

I wanted the following:

a) to be able to compose iterators at to any reasonable depth
b) that such a composition occur at compile time.
c) to permit a composition to be predefined so it could be used in
any subsequent composition.

I first considered making functions like the one you propose - 
make_?_iterator.
It didn't seem to me that it was going to satisfy the wish list as stated 
above.
Finally, I found that just by adding to each iterator adaptor a templated 
constructor of the form

// note BaseIterator DOES NOT refer to a base class.  It refers to an 
iterator
// whose behavior is going to be modified by my_iterator.

template<class BaseIterator>
my_iterator(BaseIterator &bi) : ...

I could realize all goals stated above.

This permited me to build a complex iterator such as convert binary code to 
base64 by
building and testing much simpler constituent iterators and composing them 
at compile time.
I applied it to streams of characters - but I don't think that would be any 
less useful when
applied to something like tuples.

Its described in more detail in the documenation for the serialization 
library.

Robert Ramey

David Abrahams wrote:
> Erik Åldstedt Sund <eriksund_at_[hidden]> writes:
>
>> Hi,
>>
>> just a short question: Why does not the zip_iterator header have the
>> following (or something along the lines of the following) creator
>> function:
>>
>>
>>    template <typename Iter1Type, typename Iter2Type>
>>    boost::zip_iterator<boost::tuple<Iter1Type, Iter2Type> >
>>    make_zip_iterator(Iter1Type i, Iter2Type j)
>>    {
>>      return boost::make_zip_iterator(boost::make_tuple(i, j));
>>    }
>
> Well
>
> a. we didn't think of it
>
> and
>
> b. We'd feel obliged to provide a whole series of overloads for up to
>   N iterators.
>
>>
>> That would make creating a zip_iterator much simpler.
>
> Patches welcomed, if they include documentation and tests :)