Old problem with performance

[Don]

Weed wrote:
> Weed пишет:
>> Bill Baxter пишет:
>>> On Sun, Feb 22, 2009 at 1:02 AM, Weed <resume755 at mail.ru> wrote:
>>>> Bill Baxter пишет:
>>>>> 2009/2/21 Weed <resume755 at mail.ru>:
>>>>>> Weed пишет:
>>>>>>> Bill Baxter пишет:
>>>>>>>
>>>>>>>> Why don't you just show us the class in the way you would like to
>>>>>>>> write it in C++, and we'll show you how to write it in D, or finally
>>>>>>>> agree with you that it's not possible.   But as long as you continue
>>>>>>>> to be hand-wavy about "common base classes" we're at a bit of an
>>>>>>>> impasse.  So far everyone thinks D can do what you want it to do based
>>>>>>>> on your vague descriptions.
>>>>>> As I said, you can write everything using "goto" and "if".
>>>>>>
>>>>>> ...But why you do not like the original example of this thread?
>>>>> Please post again.  I don't seem to recall any detailed example.
>>>>>
>>>>> --bb
>>>> http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digitalmars.D&artnum=83506
>>> You should use a struct there!   Your code does not show you doing
>>> anything that would even remotely suggest using a class is worthwhile.
>>>  You're doing value operations on value types.  That's what structs
>>> are for.
>>  	
>> Why?
>>
>> What if I have not substantiated the fact that c1 is a class I should
>> use there a structure?
>>
>> Used in D a model of placement classes only in heap have a rule "if you
>> made the class and trying to pass it by value is somewhere in your code,
>> there is a design error?
> 
> Explains why the question is given in this form:
> 
> I am received or wrote a classes. Is it right to overload the operator
> opAdd and use them? I think yes.
 > But why not allow this operation at the same speed that allows C++?

Actually, in D, it's really difficult to give a class value semantics.
If a, b are members of some class, consider
(1) a = a + b;
(2) a += b;
It is nearly impossible to efficiently make both of these have the same 
effect!!
You can only do it with either copy-on-write, ie, even case (2) always 
allocates; or by using a proxy class.
This is something which I consider to be a serious problem.
Much more serious than the speed issue.