Python dynamic attribute creation

[Thomas Jollans]

On 06/26/2010 05:39 AM, WANG Cong wrote:
> On 06/26/10 00:11, Neil Hodgson <nyamatongwe+thunder at gmail.com> wrote:
> 
>> WANG Cong:
>>
>>> 4) Also, this will _somewhat_ violate the OOP princples, in OOP,
>>> this is and should be implemented by inherence.
>>
>>    Most object oriented programming languages starting with Smalltalk
>> have allowed adding attributes (addInstVarName) to classes at runtime.
> 
> 
> Thanks, I have to admit that I know nothing about Smalltalk.
> 
>>From what you are saying, Smalltalk picks a way similar to setattr() in
> Python? Because you mentioned 'addInstVarName' which seems to be a
> method or a builtin function. If so, that is my point, as I mentioned
> earlier, switching to setattr() by default, instead of using assignments
> by default. :)
> 
>> Low level OOPLs like C++ and Delphi did not implement this for
>> efficiency reasons.
>>
> 
> Hmm, although this is off-topic, I am interested in this too. C++ does
> have metaprogramming, but that is actually static metaprogramming (using
> templates), not dynamic metaprogramming here. I am wondering if
> efficiency is the only reason why C++ doesn't have dynamic
> metaprogramming,

Yes, it is. I'm not quite sure how far RTTI actually goes, but I know
that performance is a key issue in the design of C++. If you have a look
at the developments toward C++0x, you will see that many new features
are being proposed - C++ is an expert's language, designed to give an
expert the most powerful tool possible, with the restriction that no new
feature may have a negative performance impact on an existing feature.
Adding actual dynamism would have a massive impact on performance and is
thus, for C++, not acceptable.

> since C++ is a static programming language I think if
> this limits C++ to implement its dynamic metaprogramming actually...
> 
> Thanks.
>