Re: New public API

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

I say - std::autoptr for collection types, std::string for scalar strings.

Krzysztof Rzymkowski wrote:

>On Tue, 2006-02-21 at 11:21 -0800, Ilya A. Volynets-Evenbakh wrote:
>  
>
>>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
>>    
>>
>
>True.
>
>  
>
>>- 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?
>>    
>>
>
>vector does simple copting, string does somthing smarter as far as I can
>see (see [2] below)
>
>  
>
>>- And finally, in ideal case, I'd prefer for public API part not to
>>depend on
>>  any external library - not even boost.
>>    
>>
>
>That is a valid point. So is std::auto_ptr the winner?
>
>  
>
>>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