division of objects into classes and structures is bad

[Don]

Andrei Alexandrescu wrote:
> Don wrote:
>> Andrei Alexandrescu wrote:
>>> Don wrote:
>>>> Christopher Wright wrote:
>>>>> Don wrote:
>>>>>> 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:
>>>>>
>>>>> The easiest way is to add an intermediate struct. This takes a fair 
>>>>> bit of manual effort, though, and prevents you from using auto.
>>>>
>>>> That particular case is the easiest possible one. The case x = y - 
>>>> x, for example, is much more difficult to recognize.
>>>>
>>>>>
>>>>> Essentially, you need a struct MyClassAddition that just records 
>>>>> operands. Then give it an implicit cast to MyClass that does the 
>>>>> work. This is an ugly solution because you need to duplicate the 
>>>>> operator overloads on MyClassXXX as well as MyClass.
>>>>>
>>>>> I believe I got this solution from an article by Andrei. It should 
>>>>> work pretty well for classes that define few overloads.
>>>>
>>>> I'm talking about a language solution. I want to solve this for the 
>>>> general case.
>>>
>>> Don't forget that the case you are solving is not general enough 
>>> because  you are focusing on eliminating temporaries, which is only 
>>> part of the story. I suggest you make place in your thoughts for loop 
>>> fusion.
>>
>> Yes. That's the classic problem for matrices, but I'm still trying to 
>> work out if it is really a general problem. I was hoping to see some 
>> new use cases, but none so far.
> 
> I think the matrices case is important enough to make it its own class 
> of problems. For example, bitmap processing is another instance of 
> matrix usefulness, just one that doesn't usually jump to mind when 
> thinking of matrices.

Yes, bitmap processing almost always uses the adjacent pixels, which 
doesn't translate naturally to BLAS operations.
The disturbing thing about both these use cases is that you normally 
want to involve other operations, such as dot product, which aren't 
operators. So an optimal solution is pretty elusive.

> Then how about BigInt and arbitrary precision numbers? Wouldn't fusing 
> some operations together be useful?

Not really, since they are rarely cache-limited.
Combining slicing operations with arithmetic might be interesting, but 
it's pretty obscure I think.