[LLVMdev] [RFC] C++11: 'virtual' and 'override'

[Pete Cooper]

On Mar 4, 2014, at 7:57 PM, Duncan P. N. Exon Smith <dexonsmith at apple.com> wrote:

> On 2014 Mar 4, at 15:01, Sean Silva <chisophugis at gmail.com> wrote:
> 
>> On Mon, Mar 3, 2014 at 2:02 AM, David Blaikie <dblaikie at gmail.com> wrote:
>> On Sun, Mar 2, 2014 at 8:19 PM, Craig Topper <craig.topper at gmail.com> wrote:
>>> While doing the conversion of LLVM_OVERRIDE to 'override' last night, I
>>> noticed that the code base is rather inconsistent on whether the 'virtual'
>>> keyword is also used when 'override' is used.
>>> 
>>> Should we have a coding standard for this? What's the preferred direction
>>> here? Seems not having 'virtual' is less overall text, but not sure how
>>> others feel.
>> 
>> My vote: omit virtual if override is used.
> 
> +1: virtual doesn’t add anything if override is present.
> 
>> (legitimate counterargument: harder to skim/match/read whether a
>> function is virtual when it's not specified and "override" appears
>> much later in the declaration)
>> 
>> One counter-datapoint: Personally, I have on at least one occasion caught myself not noticing a leading `virtual` and thinking that a method wasn't overriden because of the missing `override`. I guess the moral is that this can be pretty adaptable.
>> 
>> FWIW IMO the preferred end state is to have no useless leading `virtual`'s and using `override` for its intended purpose.
>> 
>> -- Sean Silva
>> 
>> 
>>> Related, should we require use of 'override' when methods override a base
>>> class method?
>> 
>> My vote: require override.
> 
> +1: override is useful and prevents errors.
Would it be too much to have clang emit a warning/error if override is missing?  I know that sounds crazy and people hate errors which fire too often, but there’s not too much C++11 code out there yet, and so we have a chance to put errors/warnings in now without too much pain.  People might just get used to them and think its how code has to be written :)
> 
>>> I have clang-tidy checks for both though haven't implemented fixits for them
>>> yet.
>> 
>> Cool. There has also been a suggestion that Clang could warn about
>> omitted override if at least one other member function in the same
>> class is marked override, which could get us a lot of value built into
>> the compiler (but not 'all the way', so a clang-tidy check would still
>> be appropriate).
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