Re: New public API

["Ilya A. Volynets-Evenbakh" <ilya@total-knowledge.com>]

Some more thoughts on the subject:

- retval optimization will work perfectly for single-object access
methods, but
  is far less likely to work for vectors - if they have to be filled out
from some
  other data, rather then simply copied
- We are targeting primarily GCC-based systems, so we should not rely
  on some hypothetic optimizations by compiler, but rather stick to what
  current one does. Specifically - what do we know about container copy
  constructors in libstdc++ version of STL?
- And finally, in ideal case, I'd prefer for public API part not to
depend on
  any external library - not even boost.

Krzysztof Rzymkowski wrote:

>On Mon, 2006-02-20 at 11:00 -0800, Ilya A. Volynets-Evenbakh wrote:
>  
>
>>One thing I was thinking about (and even started using in some cases)
>>is to change methods returing collections. The way it is now:
>>virtual std::vector<std::string>  getAttributeNames()
>>This means that whole vector, as well as every string inside will be copied
>>(possibly twice - inside function when creating retval, and then to the
>>actual
>>return value). Now, instead we could change signiture as follows:
>>virtual void getAttributeNames(std::vector<std::string> &out)
>>This will avoid unnessesary copying.
>>
>>Java does not have to worry about it, since it returns references, and thus
>>only one copy of object is created.
>>    
>>
>
>It is possible for a STL implementation to user reference counting in
>vector's copy constructor, thought the SGI's STL does simple copying.
>It is as well possible for the compiler to use return value optimization
>[1], thought it is not always possible to write the getters in a way
>which allows RVO. 
>
>Another option would be to use std::auto_ptr [2] or boost::shared_ptr
>[3]. 
>
>I would like to keep the API as close to the Java version as it is
>possible. So I'd rather stick with option 1 (ignore the problem) or 2
>user some sort of reference counting.
>
>[1] http://cpptips.hyperformix.com/cpptips/ret_val_opt
>[2] http://gcc.gnu.org/onlinedocs/libstdc
>++/latest-doxygen/classstd_1_1auto__ptr.html
>[3] http://www.boost.org/libs/smart_ptr/shared_ptr.htm
>
>  
>

-- 
Ilya A. Volynets-Evenbakh
Total Knowledge. CTO
http://www.total-knowledge.com