virtual-by-default rant

[Manu]

On 23 March 2012 17:24, Ary Manzana <ary at esperanto.org.ar> wrote:

> On 3/18/12 9:23 AM, Manu wrote:
>
>> The virtual model broken. I've complained about it lots, and people
>> always say "stfu, use 'final:' at the top of your class".
>>
>> That sounds tolerable in theory, except there's no 'virtual' keyword to
>> keep the virtual-ness of those 1-2 virtual functions I have... so it's
>> no good (unless I rearrange my class, breaking the logical grouping of
>> stuff in it).
>> So I try that, and when I do, it complains: "Error: variable
>> demu.memmap.MemMap.machine final cannot be applied to variable",
>> allegedly a D1 remnant.
>> So what do I do? Another workaround? Tag everything as final individually?
>>
>> My minimum recommendation: D needs an explicit 'virtual' keyword, and to
>> fix that D1 bug, so putting final: at the top of your class works, and
>> everything from there works as it should.
>>
>
> Is virtual-ness your performance bottleneck?
>

Frequently. It's often the most expensive 'trivial' operation many
processors can be asked to do. Senior programmers (who have much better
things to waste their time on considering their pay bracket) frequently
have to spend late nights mitigating this even in C++ where virtual isn't
default. In D, I'm genuinely concerned by this prospect. Now I can't just
grep for virtual and fight them off, which is time consuming alone, I will
need to take every single method, one by one, prove it is never overloaded
anywhere (hard to do), before I can even begin the normal process of
de-virtualising it like you do in C++.
The problem is elevated by the fact that many programmers are taught in
university that virtual functions are okay. They come to the company, write
code how they were taught in university, and then we're left to fix it up
on build night when we can't hold our frame rate. virtual functions and
scattered/redundant memory access are usually the first thing you go
hunting for. Fixing virtuals is annoying when the system was designed to
exploit them, it often requires some extensive refactoring, much harder to
fix than a bad memory access pattern, which might be as simple as
rearranging a struct.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.puremagic.com/pipermail/digitalmars-d/attachments/20120323/b07cef21/attachment.html>