division of objects into classes and structures is bad

[Don]

Weed wrote:
> Don пишет:
>> Weed wrote:
>>> Denis Koroskin пишет:
>>>
>>>>>  80490eb:       8d 85 6c fe ff ff       lea    -0x194(%ebp),%eax
>>>>>  80490f1:       50                      push   %eax
>>>>>  80490f2:       8d 85 2c fb ff ff       lea    -0x4d4(%ebp),%eax
>>>>>  80490f8:       e8 67 ff ff ff          *call   8049064*
>>>>>  80490fd:       e8 62 ff ff ff          *call   8049064*
>>>>>     return c2.i;
>>>>>  8049102:       8b 85 cc fc ff ff       mov    -0x334(%ebp),%eax
>>>>> ...
>>>>>
>>>>>
>>>>> (in 80490f8 and 80490fd simply two calls successively)
>>>>>
>>>>> If structures and classes were same that excellent optimization in any
>>>>> case would turn out
>>>> If that's your use case, then your should seriosly reconsider using
>>>> struct instead of class for your objects.
>>> Classes always give such overhead if them to use in such quality. For
>>> example, classes basically cannot be used as any mathematical objects
>>> using overload of arithmetics. But also not only arithmetics, it it is
>>> simple as a good example.
>>>
>>>> Alternatively, you can use +=
>>>> instead.
>>> Here yes, but if I add classes of different types? Then not to escape
>>> any more from creation of the temporary object in the heap.
>>>
>>>> Other than that, this is not a convincing argument.
>>>>
>>>> Reading many of your posts I came to a conclusion that you are
>>>> shortsighted and too crazy about performance. What you care about is a
>>>> premature optimization, which is a root of all the evil. You should
>>>> ensure that your programm is complete and correct, first and *then*
>>>> start doing profiling and optimizations.
>>> The program is already ready. It entirely consists of the various
>>> mathematics. Approximately %30 times of performance are spent for
>>> similar superfluous work. On C++ the program will work on %30 faster (I
>>> hope :)) and on D I am will turn out to do nothing with it.
>>>
>>>
>>>> Going back to the topic, dividing user types into two cathegories
>>>> (structs and classes) is considered modern and right.
>>> I do not accept such argument:)
>>>
>>>> Some languages
>>>> lack structs support at all (e.g. Java), but structs are too useful for
>>>> optimization and language interoperation to drop them in a systems
>>>> programming language. Some lack classes and try doing everything with
>>>> structs (C). D takes the best of both worlds.
>>> Probably I have not understood something, but I do not suggest to refuse
>>> structures in general. I suggest to allow to create classes on a stack
>>> as it is made in C++. That is actually to make structures and classes
>>> same, than they and are, for example, in C++.
>>>
>>> In the initial message I have shown that for perfomance important that
>>> the class could be transferred and on value. And it not artful premature
>>> optimisation - objects on value always so are transferred, all
>>> programmers know it and use when do not wish to allocate a place in a
>>> heap, that is usually always when the object will live in {}.
>>>
>>> Besides, a class in a stack it is normal - keyword addition "scope" for
>>> classes too speaks about it.
>>>
>>> Rigidly having divided classes and structures D deprives of the
>>> programmer of some possibilities which give it C++-like languages. I
>>> consider that such languages should give all possibilities which allows
>>> CPU but hiding concrete architecture, otherwise I would choose less
>>> difficult in use language.
>> Use classes if you want polymorphism. Otherwise, use structs. It's a
>> clear distinction, which is not at all arbitrary -- there are
>> significant implications for the generated code.
> 
> And if polymorphism is necessary and such calculations are necessary as
> I have above described? To emulate polymorphism with the mixins? Or
> simply to reconcile to such obvious losses?
> 
> I about that that division into classes and structures in language D
> automatically reduce perfomance of programs. Unlike languages where this
> division is not present (C++).

I agree with you that there's a problem, but I think you're wrong about 
the solution. C++ suffers from severe problems with creation of 
temporaries in expressions. The problem occurs whenever you have heap 
allocations inside an object which does operator overloading. Sure, in 
the simple case you mentioned, using a struct works because the size of 
the data is small. But it general, it's not possible to avoid the heap 
allocation, and so in C++ you'll still have a problem.

The creation of temporaries during expressions is something I'm 
currently working on solving. The case you mentioned is addressed by a 
proposal I made long ago:
http://d.puremagic.com/issues/show_bug.cgi?id=124

  c2 = c1 + c1 + c1;

would be transformed into
t1 = c1 + c1;
t1.opAddAssign(c1);
c2 = t1;
which gets rid of the temporary heap allocation.
I don't think you could ever get rid of the heap allocation for c2 since
(a) c2 might be null, initially; and (b) c2 might be pointing to the 
same place as c1.

Nonetheless, I'd like to do better than this.
Consider:
C c1, c2, c3;
c3 = c1*5 + c2/6;

The optimal solution depends on whether in-place operations are possible 
or not. Interestingly, X+=Y is more efficient than X=X+Y only if 
in-place operations are possible; there's no point in defining it if 
in-place is impossible.

Case 1: in-place operations are possible, += exists. All operators 
include destination.
Convert to t1 = c2/6; c3 = c1*5;  c3+=t1;
---
LocalHeap h;
t1 = h.new(C);  // create on LocalHeap h
t1.operatorWithDestination("/")(c2, 6);
C t2 = new C;  // create on heap
t2.operatorWithDestination!("*")(c1, 5);
c3 = t2.operatorAssign!("+")(t1); // in-place += operation on heap
h.releaseAll;
---
Case 2: in-place operations are impossible, += doesn't exist.
---
LocalHeap h;
t1 = c1.operatorTemporary!("*")(5, h); // create on local heap
t2 = c2.operatorTemporary!("/")(6, h); // create on local heap
c3 = t1.operator!("+")(t2); // create on heap
h.releaseAll;
---
It's far too complicated at present to be workable, but that's the basic 
idea.