Re: [boost] [gil io_new review] Reading images from in-memory sources

Subject: Re: [boost] [gil io_new review] Reading images from in-memory sources
From: Mateusz Loskot (mateusz_at_[hidden])
Date: 2010-12-06 12:56:20

On 06/12/10 17:28, Kenny Riddile wrote:
> On 12/6/2010 11:26 AM, Mateusz Loskot wrote:
>> On 06/12/10 16:21, Kenny Riddile wrote:
>>> On 12/6/2010 10:10 AM, Christian Henning wrote:
>>>>>
>>>>> I accomplish this using Boost.IOStreams...something like this works
>>>>> for me:
>>>>>
>>>>> using namespace boost::iostreams;
>>>>> stream< array_source> bufferStream( buffer, size );
>>>>> read_image( bufferStream, dest, jpeg_tag() );
>>>>
>>>>
>>>> Cool this is what I was looking for. No extra copying involved?
>>>
>>> From the IOStreams documentation on array_source:
>>>
>>> "Model of Source providing read-only access to a sequence of characters
>>> in memory."
>>>
>>> doesn't sound like any copying to me :)
>>
>> I'm afraid this is your interpretation.
>> This statement does not say anything about copying.
>> It only states read-only access is performed.
>> It is possible read-only access is performed against a copy of data.
>
>
> I agree that it's just my interpretation and I haven't verified that
> interpretation. Still I think it is likely to be a common
> interpretation, and one that is only incorrect if the author of the
> documentation was intentionally trying to be confusing and/or the
> library author was doing something silly.

I am not sure about it.
IMO, the situation is is similar to standard algorithms and predicates:
if a semantic is not specified in details, any valid semantic is 
possible in terms of presented function prototype/class definition, etc.

Reading about std::remove_if in copy of the n3092, I don't see a word
about specific move/copy requirements of predicate, however, the
algorithm is free to make number of copies of the predicate internally.

Back to the Boost.IOStreams, indeed, the docs are incomplete [1]
but as the the author explained on the list, the devices (Source is a 
device) does not have to follow "must be copy-constructibile" but they
"can be non-copyable", what means that some may be copyable as well.

[1] http://lists.boost.org/Archives/boost/2005/11/96479.php
[2] http://lists.boost.org/Archives/boost/2005/10/95939.php

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net
Charter Member of OSGeo, http://osgeo.org
Member of ACCU, http://accu.org