Re: [Boost-Users] Re: How to use Iterator Adaptors?

From: Duane Murphy (duanemurphy_at_[hidden])
Date: 2002-06-04 09:48:38

--- At Tue, 4 Jun 2002 07:25:05 -0700, Duane Murphy wrote:

>--- At Tue, 4 Jun 2002 09:45:12 -0400, David Abrahams wrote:
>>"Duane Murphy" <duanemurphy_at_[hidden]> wrote in message
>>news:20020604050249.610_at_mail.murphyslogic.com...
>>> --- At Tue, 4 Jun 2002 00:05:46 -0400, David Abrahams wrote:
>>> I dont have any iterator to assign policies to yet.
>>
>>The policies are supposed to implement the core operations of the iterator
>>using the Base object. You can, of course, stick the neccessary
>>functionality in the Base object and use the default policies, as you are
>>doing, but it seems a little unnatural to me.
>>
>>> This is usually a forward iterator if copying
>>> is practical given the nature of the API. Basically in the example, the
>>> iterator would hold a DIR structure and use the standard DIR APIs to
>>> "increment" and dereference the structure as required.
>>>
>>> So, what is the "normal" way of creating an iterator out of thin air as
>>> it were?
>>
>>If you have a DIR structure, I would use that as the Base object directly,
>>then write a Policies class which implements the operations on it.
>
>[ Giant light bulb goes on! ] 
>
>Now I get it. Thank you very much for this explaination. 
>
>Everytime I write an iterator there is almost always some data structure
>that is required in the iterator for me to use. You have simply
>"constructed" that part of the iterator through the base template
>parameter. I have been working way to hard to make this work.
>
>When I first did things this way, I went and wrapped some data structure
>in all kinds of methods. I see now that I was making too much work for
>myself. Simply specify the object that is the base and access it
>directly; no additional objects needed. Treating base as a member
>variable is acceptable.

Member variable isnt exactly the right terminology. Maybe, using base as
a data structure rather than an object would be more correct.

>Thank you for this enlightening discussion. I will follow this pattern
>for my future iterators.

 ...Duane