[llvm-dev] Variable names rule

Nicolai Hähnle via llvm-dev llvm-dev at lists.llvm.org
Mon Feb 4 08:10:42 PST 2019

On 04.02.19 15:20, via llvm-dev wrote:
> I'd much rather have a convention that did not treat all "variables" the 
> same. Instead, distinguish variable names based on scope/lifetime;

While it's not a very strong opinion, I'm actually fond of the fact that 
they're the same.

The reason is that when you're implementing passes, whether a variable 
is local to the current method or a member of the class is really not a 
very meaningful distinction, and it's convenient to be able to change 
the scope occasionally as part of refactorings.

IDEs are very good at jumping to variable declarations if there's any doubt.


> for 
> example, it's common practice (outside of LLVM) for class data members 
> to have a different/variant convention (trailing underscore, leading 
> "m_") because that data all has a scope/lifetime far beyond the current 
> method.  Local variables and function parameters, by contrast, have 
> comparatively limited scope.  With no immediate visual clue to the 
> difference, I find myself spending a fair amount of time paging around 
> the source and trolling through headers trying to work out which is 
> what.  That is: I find the current convention not very readable.
> So, I'm quite happy to have camelCase for variables, but would also like 
> some other distinction within the universe of variable names.
> Of course any change to existing conventions would cause some churn and 
> confusion, but we *already* have that, as the current nominal 
> conventions aren't in place in the entire codebase.
> Regarding snake_case, LLVM has very limited use of that, and only for 
> things that are (a) substitutes or (b) extensions of STL features.  
> "iterator_range" for example.  camelCase predominates.
> --paulr
> *From:*llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of 
> *Chris Lattner via llvm-dev
> *Sent:* Saturday, February 02, 2019 11:19 PM
> *To:* Michael Platings
> *Cc:* llvm-dev at lists.llvm.org; nd
> *Subject:* Re: [llvm-dev] Variable names rule
> On Feb 2, 2019, at 8:18 PM, Chris Lattner <clattner at nondot.org 
> <mailto:clattner at nondot.org>> wrote:
> On Feb 1, 2019, at 6:20 AM, Michael Platings via llvm-dev 
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
> Hi all,
> As application of the naming rules are currently under discussion [1] 
> this seems like a good time to bring this up:
> The current variable naming rule [2] states: Variable names should be 
> nouns (as they represent state). The name should be camel case, and 
> start with an upper case letter (e.g. Leader or Boats).
> I'm a relatively new arrival to the LLVM codebase and I want to follow 
> the rules wherever I can, but I humbly submit that this rule is 
> suboptimal for readable code.
> The rationale given at the time this rule was added was "document the 
> prevailing convention" [3].
> I completely agree with you that our variable naming rule is broken. 
>   This discussion has been brought up before (e.g. 
> http://lists.llvm.org/pipermail/llvm-dev/2014-October/077685.html) and 
> hasn’t made any progress - people seem to not be willing to make a 
> change, e.g. saying "the cure is worse than the disease".  I’m 
> personally in favor of Nick’s proposal (linked above) which makes 
> variable names and function names be lower camel case.
> It’s worth noting that at the time, if I recall correctly, I argued 
> against Nick’s proposal.  I’m since come around to see the wisdom of his 
> position and agree that we should have done it.
> -Chris
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Aber vergiss niemals, wie sie sein sollte.

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