[Liblas-devel] Design/architecture questions

[Mateusz Loskot]

On 30/11/10 16:57, Howard Butler wrote:
> On Nov 30, 2010, at 9:50 AM, Michael Gerlek wrote:
>>
>> 2. Auto_ptr is used for ReaderImpl and some others.  What is the
>> intent here?
>
> I hope Mateusz can chime in on this one.  I never fully understood
> the intent here, but I'm kind of a dolt on these things.

Are you asking why the auto_ptr in particular or why smart
pointer at all?

Initially, the Reader and ReaderImpl were designed based
on the PIMPL (handle-body) idiom. It is still true,
but handle has lost it's lightweight and become a semi-body now.

The reason is simple: RAII and no need for managing lifetime of the body
object. It doesn't have to be auto_ptr, but any scope-friendly smart
pointer. auto_ptr is available in the standard library and
works very well, so I use it.

>> One could imagine (and Howard suggested) a factory which spits out
>>  ReaderI's based on given inputs (based on file extensions or magic
>>  numbers or whathaveyou, see next question).
>
> Mateusz had taken on some of this effort, but backed off after it
> became apparent that it would require tearing apart a number of
> things.  I hope he can explain what he thinks might be needed to
> pick this back up.

My idea was to the make the Reader a ref-counted handle, thus
copyable and assignable. Then factory returns this lightweight handle.
However, the Reader has become fat, then this idea is more or less blocked.

A poor solution could be to employ boost::shared_ptr<Reader> to provide 
the ref-counted lightweight object returned from factory and passed 
around, but I don't like such "handle to handle to body" stack at all, 
so I've given up.

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