Thank you very much for the feedbacks.

On Thu, Dec 20, 2018 at 4:52 AM Konstantin Tokarev <annulen@yandex.ru> wrote:

19.12.2018, 12:53, "Fujii Hironori" <fujii.hironori@gmail.com>:
> I'd like to change this because 'final' doesn't necessarily imply
> 'override'. See the following stackoverflow:
> https://stackoverflow.com/questions/29412412/does-final-imply-override

It does imply override, unless it is used in a declaration of new virtual method
(which has no practical meaning fwiw)

You are right. C++ allows using 'final' with 'virtual' without overriding.
Even though I don't know practical use-cases for it, C++ allows it because 'final' doesn't mean overriding.
And, this is the only reason 'final' doesn't necessarily imply override.
This is a kind of chicken egg problem. I don't know which is true:

1. C++ allows it because 'final' doesn't mean overriding.
2. 'final' doesn't necessarily imply override because C++ allows it

On Thu, Dec 20, 2018 at 6:28 AM Konstantin Tokarev <annulen@yandex.ru> wrote:


19.12.2018, 23:27, "Michael Catanzaro" <mcatanzaro@igalia.com>:
> On Wed, Dec 19, 2018 at 1:58 PM, Konstantin Tokarev <annulen@yandex.ru>
> wrote:
>>  Adding override to method which already has final specifier doesn't
>>  affect anything,
>>  because both final and override may ony be used on virtual methods
>
> FWIW I prefer override because it's much more clear what that keyword
> is used for.

If class itself has "final" specifier, "override" on methods works in the same way
as "final", and I agree that it conveys intention more clear.

I think so, especially after I will update the code style guidelines in Bug 192844.

Bug 192844 – Update code style guidelines for using 'final' specifier for all classes which has no derived classes

 
However, Darin in [1]
suggested that we use "final" aggressively to avoid accidentally losing compiler
optimization (i.e. devirtualization of call)

[1] https://lists.webkit.org/pipermail/webkit-dev/2016-March/028022.html

I think this won't be a problem after all classes which has no derived classes are capped with 'final'. 
 

On Thu, Dec 20, 2018 at 7:42 AM <Ross.Kirsling@sony.com> wrote:
In that case, I'll point out that C++ Core Guidelines has a rule "Virtual functions should specify exactly one of virtual, override, or final".
(http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rh-override)

Their tl;dr:
"
        • virtual means exactly and only “this is a new virtual function.”
        • override means exactly and only “this is a non-final overrider.”
        • final means exactly and only “this is a final overrider.”
"

FWIW, they also have a rule "Use final sparingly" with the note that "Claims of performance improvements from final should be substantiated."
(http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rh-final)


C.128 is a same rule with the current WebKit coding style guidelines.
But, I think C.128 makes sense with C.139.
C.139 is against to Bug 192844.
After Bug 192844 update, we will have a lot of 'final' classes, not sparignly.